Require Import Unicode.Utf8.

Module No1.
Import Unicode.Utf8.
  (*We first give the axioms of Principia
for the propositional calculus in *1.*)

Axiom MP1_1 : ∀  P Q : Prop,
  (P → Q) → P → Q. (*Modus ponens*)

  (**1.11 ommitted: it is MP for propositions containing variables. Likewise, ommitted the well-formedness rules 1.7, 1.71, 1.72*)

Axiom Taut1_2 : ∀ P : Prop, 
  P ∨ P→ P. (*Tautology*)

Axiom Add1_3 : ∀ P Q : Prop, 
  Q → P ∨ Q. (*Addition*)

Axiom Perm1_4 : ∀ P Q : Prop, 
  P ∨ Q → Q ∨ P. (*Permutation*)

Axiom Assoc1_5 : ∀ P Q R : Prop, 
  P ∨ (Q ∨ R) → Q ∨ (P ∨ R).

Axiom Sum1_6: ∀ P Q R : Prop, 
  (Q → R) → (P ∨ Q → P ∨ R). (*These are all the propositional axioms of Principia Mathematica.*)

Axiom Impl1_01 : ∀ P Q : Prop, 
  (P → Q) = (~P ∨ Q). (*This is a definition in Principia: there → is a defined sign and ∨, ~ are primitive ones. So we will use this axiom to switch between disjunction and implication.*)

End No1.

Module No2.
Import No1.

(*We proceed to the deductions of of Principia.*)

Theorem Abs2_01 : ∀ P : Prop,
  (P → ~P) → ~P.
Proof. intros P.
  specialize Taut1_2 with (~P).
  replace (~P ∨ ~P) with (P → ~P).
  apply MP1_1.
  apply Impl1_01.
Qed.

Theorem n2_02 : ∀ P Q : Prop, 
  Q → (P → Q).
Proof. intros P Q.
  specialize Add1_3 with (~P) Q.
  replace (~P ∨ Q) with (P → Q).
  apply (MP1_1 Q (P → Q)).
  apply Impl1_01.
Qed.

Theorem n2_03 : ∀ P Q : Prop,
  (P → ~Q) → (Q → ~P).
Proof. intros P Q.
  specialize Perm1_4 with (~P) (~Q).
  replace (~P ∨ ~Q) with (P → ~Q). 
  replace (~Q ∨ ~P) with (Q → ~P).
  apply (MP1_1 (P → ~Q) (Q → ~P)).
  apply Impl1_01.
  apply Impl1_01.
Qed.

Theorem Comm2_04 : ∀ P Q R : Prop,
  (P → (Q → R)) → (Q → (P → R)).
Proof. intros P Q R.
  specialize Assoc1_5 with (~P) (~Q) R.
  replace (~Q ∨ R) with (Q → R).
  replace (~P ∨ (Q → R)) with (P → (Q → R)).
  replace (~P ∨ R) with (P → R).
  replace (~Q ∨ (P → R)) with (Q → (P → R)).
  apply (MP1_1 (P → Q → R) (Q → P → R)).
  apply Impl1_01. 
  apply Impl1_01.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem Syll2_05 : ∀ P Q R : Prop,
  (Q → R) → ((P  → Q) → (P → R)).
Proof. intros P Q R.
  specialize Sum1_6 with (~P) Q R.
  replace (~P ∨ Q) with (P → Q). 
  replace (~P ∨ R) with (P → R).
  apply (MP1_1 (Q → R) ((P → Q) → (P → R))).
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem Syll2_06 : ∀ P Q R : Prop,
  (P → Q) → ((Q → R) → (P → R)).
Proof. intros P Q R. 
  specialize Comm2_04 with (Q → R) (P → Q) (P → R). 
  intros Comm2_04.
  specialize Syll2_05 with P Q R. 
  intros Syll2_05.
  specialize MP1_1 with ((Q → R) → (P → Q) → P → R) ((P → Q) → ((Q → R) → (P → R))). 
  intros MP1_1.
  apply MP1_1.
  apply Comm2_04.
  apply Syll2_05.
Qed.

Theorem n2_07 : ∀ P : Prop,
  P → (P ∨ P).
Proof. intros P.
  specialize Add1_3 with P P.
  apply MP1_1.
Qed.

Theorem n2_08 : ∀ P : Prop,
  P → P.
Proof. intros P.
  specialize Syll2_05 with P (P ∨ P) P. 
  intros Syll2_05.
  specialize Taut1_2 with P. 
  intros Taut1_2.
  specialize MP1_1 with ((P ∨ P) → P) (P → P). 
  intros MP1_1.
  apply Syll2_05.
  apply Taut1_2.
  apply n2_07.
Qed.

Theorem n2_1 : ∀ P : Prop,
  (~P) ∨ P.
Proof. intros P.
  specialize n2_08 with P. 
  replace (~P ∨ P) with (P → P).
  apply MP1_1.
  apply Impl1_01.
Qed.

Theorem n2_11 : ∀ P : Prop,
  P ∨ ~P.
Proof. intros P.
  specialize Perm1_4 with (~P) P. 
  intros Perm1_4.
  specialize n2_1 with P. 
  intros Abs2_01.
  apply Perm1_4.
  apply n2_1.
Qed.

Theorem n2_12 : ∀ P : Prop,
  P → ~~P.
Proof. intros P.
  specialize n2_11 with (~P). 
  intros n2_11.
  rewrite Impl1_01. 
  assumption.
Qed.

Theorem n2_13 : ∀ P : Prop,
  P ∨ ~~~P.
Proof. intros P.
  specialize Sum1_6 with P (~P) (~~~P). 
  intros Sum1_6.
  specialize n2_12 with (~P). 
  intros n2_12.
  apply Sum1_6.
  apply n2_12.
  apply n2_11.
Qed.

Theorem n2_14 : ∀ P : Prop,
  ~~P → P.
Proof. intros P.
  specialize Perm1_4 with P (~~~P). 
  intros Perm1_4.
  specialize n2_13 with P. 
  intros n2_13.
  rewrite Impl1_01.
  apply Perm1_4.
  apply n2_13.
Qed.

Theorem Trans2_15 : ∀ P Q : Prop,
  (~P → Q) → (~Q → P).
Proof. intros P Q.
  specialize Syll2_05 with (~P) Q (~~Q). 
  intros Syll2_05a.
  specialize n2_12 with Q. 
  intros n2_12.
  specialize n2_03 with (~P) (~Q). 
  intros n2_03.
  specialize Syll2_05 with (~Q) (~~P) P. 
  intros Syll2_05b.
  specialize Syll2_05 with (~P → Q) (~P → ~~Q) (~Q → ~~P). 
  intros Syll2_05c.
  specialize Syll2_05 with (~P → Q) (~Q → ~~P) (~Q → P). 
  intros Syll2_05d.
  apply Syll2_05d.
  apply Syll2_05b.
  apply n2_14.
  apply Syll2_05c.
  apply n2_03.
  apply Syll2_05a.
  apply n2_12.
Qed.

Ltac Syll H1 H2 S :=
  let S := fresh S in match goal with 
    | [ H1 : ?P → ?Q, H2 : ?Q → ?R |- _ ] =>
       assert (S : P → R) by (intros p; apply (H2 (H1 p)))
end. 

Ltac MP H1 H2 :=
  match goal with 
    | [ H1 : ?P → ?Q, H2 : ?P |- _ ] => specialize (H1 H2)
end.

Theorem Trans2_16 : ∀ P Q : Prop,
  (P → Q) → (~Q → ~P).
Proof. intros P Q.
  specialize n2_12 with Q. 
  intros n2_12a.
  specialize Syll2_05 with P Q (~~Q). 
  intros Syll2_05a.
  specialize n2_03 with P (~Q). 
  intros n2_03a.
  MP n2_12a Syll2_05a.
  Syll Syll2_05a n2_03a S.
  apply S.
Qed.

Theorem Trans2_17 : ∀ P Q : Prop,
  (~Q → ~P) → (P → Q).
Proof. intros P Q.
  specialize n2_03 with (~Q) P. 
  intros n2_03a.
  specialize n2_14 with Q. 
  intros n2_14a.
  specialize Syll2_05 with P (~~Q) Q. 
  intros Syll2_05a.
  MP n2_14a Syll2_05a.
  Syll n2_03a Syll2_05a S.
  apply S.
Qed.

Theorem n2_18 : ∀ P : Prop,
  (~P → P) → P.
Proof. intros P.
  specialize n2_12 with P.
  intro n2_12a.
  specialize Syll2_05 with (~P) P (~~P). 
  intro Syll2_05a.
  MP Syll2_05a n2_12.
  specialize Abs2_01 with (~P). 
  intros Abs2_01a.
  Syll Syll2_05a Abs2_01a Sa.
  specialize n2_14 with P. 
  intros n2_14a.
  Syll H n2_14a Sb.
  apply Sb.
Qed.

Theorem n2_2 : ∀ P Q : Prop,
  P → (P ∨ Q).
Proof. intros P Q.
  specialize Add1_3 with Q P. 
  intros Add1_3a.
  specialize Perm1_4 with Q P. 
  intros Perm1_4a.
  Syll Add1_3a Perm1_4a S.
  apply S.
Qed.

Theorem n2_21 : ∀ P Q : Prop,
  ~P → (P → Q).
Proof. intros P Q.
  specialize n2_2 with (~P) Q. 
  intros n2_2a.
  specialize Impl1_01 with P Q. 
  intros Impl1_01a.
  replace (~P∨Q) with (P→Q) in n2_2a.
  apply n2_2a.
Qed.

Theorem n2_24 : ∀ P Q : Prop,
  P → (~P → Q).
Proof. intros P Q.
  specialize n2_21 with P Q. 
  intros n2_21a.
  specialize Comm2_04 with (~P) P Q. 
  intros Comm2_04a.
  apply Comm2_04a.
  apply n2_21a.
Qed.

Theorem n2_25 : ∀ P Q : Prop,
  P ∨ ((P ∨ Q) → Q).
Proof. intros P Q.
  specialize n2_1 with (P ∨ Q).
  intros n2_1a.
  specialize Assoc1_5 with (~(P∨Q)) P Q. 
  intros Assoc1_5a.
  MP Assoc1_5a n2_1a.
  replace (~(P∨Q)∨Q) with (P∨Q→Q) in Assoc1_5a.
  apply Assoc1_5a.
  apply Impl1_01.
Qed.

Theorem n2_26 : ∀ P Q : Prop,
  ~P ∨ ((P → Q) → Q).
Proof. intros P Q.
  specialize n2_25 with (~P) Q. 
  intros n2_25a.
  replace (~P∨Q) with (P→Q) in n2_25a.
  apply n2_25a.
  apply Impl1_01.
Qed.

Theorem n2_27 : ∀ P Q : Prop,
  P → ((P → Q) → Q).
Proof. intros P Q.
  specialize n2_26 with P Q. 
  intros n2_26a.
  replace (~P∨((P→Q)→Q)) with (P→(P→Q)→Q) in n2_26a.
  apply n2_26a.
  apply Impl1_01.
Qed.

Theorem n2_3 : ∀ P Q R : Prop,
  (P ∨ (Q ∨ R)) → (P ∨ (R ∨ Q)).
Proof. intros P Q R.
  specialize Perm1_4 with Q R. 
  intros Perm1_4a.
  specialize Sum1_6 with P (Q∨R) (R∨Q). 
  intros Sum1_6a.
  MP Sum1_6a Perm1_4a.
  apply Sum1_6a.
Qed.

Theorem n2_31 : ∀ P Q R : Prop,
  (P ∨ (Q ∨ R)) → ((P ∨ Q) ∨ R).
Proof. intros P Q R.
  specialize n2_3 with P Q R. 
  intros n2_3a.
  specialize Assoc1_5 with P R Q. 
  intros Assoc1_5a.
  specialize Perm1_4 with R (P∨Q). 
  intros Perm1_4a.
  Syll Assoc1_5a Perm1_4a Sa.
  Syll n2_3a Sa Sb.
  apply Sb.
Qed.

Theorem n2_32 : ∀ P Q R : Prop,
  ((P ∨ Q) ∨ R) → (P ∨ (Q ∨ R)).
Proof. intros P Q R.
  specialize Perm1_4 with (P∨Q) R. 
  intros Perm1_4a.
  specialize Assoc1_5 with R P Q. 
  intros Assoc1_5a.
  specialize n2_3 with P R Q. 
  intros n2_3a.
  specialize Syll2_06 with ((P∨Q)∨R) (R∨P∨Q) (P∨R∨Q). 
  intros Syll2_06a.
  MP Syll2_06a Perm1_4a.
  MP Syll2_06a Assoc1_5a.
  specialize Syll2_06 with ((P∨Q)∨R) (P∨R∨Q) (P∨Q∨R). 
  intros Syll2_06b.
  MP Syll2_06b Syll2_06a.
  MP Syll2_06b n2_3a.
  apply Syll2_06b.
Qed.

Axiom n2_33 : ∀ P Q R : Prop,
  (P∨Q∨R)=((P∨Q)∨R). (*This definition makes the default left association. The default in Coq is right association, so this will need to be applied to underwrite some inferences.*)

Theorem n2_36 : ∀ P Q R : Prop,
  (Q → R) → ((P ∨ Q) → (R ∨ P)).
Proof. intros P Q R.
  specialize Perm1_4 with P R. 
  intros Perm1_4a.
  specialize Syll2_05 with (P∨Q) (P∨R) (R∨P). 
  intros Syll2_05a.
  MP Syll2_05a Perm1_4a.
  specialize Sum1_6 with P Q R. 
  intros Sum1_6a.
  Syll Sum1_6a Syll2_05a S.
  apply S.
Qed.

Theorem n2_37 : ∀ P Q R : Prop,
  (Q → R) → ((Q ∨ P) → (P ∨ R)).
Proof. intros P Q R.
  specialize Perm1_4 with Q P. 
  intros Perm1_4a.
  specialize Syll2_06 with (Q∨P) (P∨Q) (P∨R). 
  intros Syll2_06a.
  MP Syll2_05a Perm1_4a.
  specialize Sum1_6 with P Q R. 
  intros Sum1_6a.
  Syll Sum1_6a Syll2_05a S.
  apply S.
Qed.

Theorem n2_38 : ∀ P Q R : Prop,
  (Q → R) → ((Q ∨ P) → (R ∨ P)).
Proof. intros P Q R.
  specialize Perm1_4 with P R. 
  intros Perm1_4a.
  specialize Syll2_05 with (Q∨P) (P∨R) (R∨P). 
  intros Syll2_05a.
  MP Syll2_05a Perm1_4a.
  specialize Perm1_4 with Q P. 
  intros Perm1_4b.
  specialize Syll2_06 with (Q∨P) (P∨Q) (P∨R). 
  intros Syll2_06a.
  MP Syll2_06a Perm1_4b.
  Syll Syll2_06a Syll2_05a H.
  specialize Sum1_6 with P Q R. 
  intros Sum1_6a.
  Syll Sum1_6a H S.
  apply S.
Qed.

Theorem n2_4 : ∀ P Q : Prop,
  (P ∨ (P ∨ Q)) → (P ∨ Q).
Proof. intros P Q.
  specialize n2_31 with P P Q. 
  intros n2_31a.
  specialize Taut1_2 with P. 
  intros Taut1_2a.
  specialize n2_38 with Q (P∨P) P. 
  intros n2_38a.
  MP n2_38a Taut1_2a.
  Syll n2_31a n2_38a S.
  apply S.
Qed.

Theorem n2_41 : ∀ P Q : Prop,
  (Q ∨ (P ∨ Q)) → (P ∨ Q).
Proof. intros P Q.
  specialize Assoc1_5 with Q P Q. 
  intros Assoc1_5a.
  specialize Taut1_2 with Q. 
  intros Taut1_2a.
  specialize Sum1_6 with P (Q∨Q) Q. 
  intros Sum1_6a.
  MP Sum1_6a Taut1_2a.
  Syll Assoc1_5a Sum1_6a S.
  apply S.
Qed.

Theorem n2_42 : ∀ P Q : Prop,
  (~P ∨ (P → Q)) → (P → Q).
Proof. intros P Q.
  specialize n2_4 with (~P) Q. 
  intros n2_4a.
  replace (~P∨Q) with (P→Q) in n2_4a.
  apply n2_4a. apply Impl1_01.
Qed.

Theorem n2_43 : ∀ P Q : Prop,
  (P → (P → Q)) → (P → Q).
Proof. intros P Q.
  specialize n2_42 with P Q. 
  intros n2_42a.
  replace (~P ∨ (P→Q)) with (P→(P→Q)) in n2_42a.
  apply n2_42a. 
  apply Impl1_01.
Qed.

Theorem n2_45 : ∀ P Q : Prop,
  ~(P ∨ Q) → ~P.
Proof. intros P Q.
  specialize n2_2 with P Q. 
  intros n2_2a.
  specialize Trans2_16 with P (P∨Q). 
  intros Trans2_16a.
  MP n2_2 Trans2_16a.
  apply Trans2_16a.
Qed.

Theorem n2_46 : ∀ P Q : Prop,
  ~(P ∨ Q) → ~Q.
Proof. intros P Q.
  specialize Add1_3 with P Q. 
  intros Add1_3a.
  specialize Trans2_16 with Q (P∨Q). 
  intros Trans2_16a.
  MP Add1_3a Trans2_16a.
  apply Trans2_16a.
Qed.

Theorem n2_47 : ∀ P Q : Prop,
  ~(P ∨ Q) → (~P ∨ Q).
Proof. intros P Q.
  specialize n2_45 with P Q. 
  intros n2_45a.
  specialize n2_2 with (~P) Q. 
  intros n2_2a.
  Syll n2_45a n2_2a S.
  apply S.
Qed.

Theorem n2_48 : ∀ P Q : Prop,
  ~(P ∨ Q) → (P ∨ ~Q).
Proof. intros P Q.
  specialize n2_46 with P Q. 
  intros n2_46a.
  specialize Add1_3 with P (~Q). 
  intros Add1_3a.
  Syll n2_46a Add1_3a S.
  apply S.
Qed.

Theorem n2_49 : ∀ P Q : Prop,
  ~(P ∨ Q) → (~P ∨ ~Q).
Proof. intros P Q.
  specialize n2_45 with P Q. 
  intros n2_45a.
  specialize n2_2 with (~P) (~Q). 
  intros n2_2a.
  Syll n2_45a n2_2a S.
  apply S.
Qed.

Theorem n2_5 : ∀ P Q : Prop,
  ~(P → Q) → (~P → Q).
Proof. intros P Q.
  specialize n2_47 with (~P) Q. 
  intros n2_47a.
  replace (~P∨Q) with (P→Q) in n2_47a.
  replace (~~P∨Q) with (~P→Q) in n2_47a.
  apply n2_47a.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n2_51 : ∀ P Q : Prop,
  ~(P → Q) → (P → ~Q).
Proof. intros P Q.
  specialize n2_48 with (~P) Q. 
  intros n2_48a.
  replace (~P∨Q) with (P→Q) in n2_48a.
  replace (~P∨~Q) with (P→~Q) in n2_48a.
  apply n2_48a.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n2_52 : ∀ P Q : Prop,
  ~(P → Q) → (~P → ~Q).
Proof. intros P Q.
  specialize n2_49 with (~P) Q. 
  intros n2_49a.
  replace (~P∨Q) with (P→Q) in n2_49a.
  replace (~~P∨~Q) with (~P→~Q) in n2_49a.
  apply n2_49a.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n2_521 : ∀ P Q : Prop,
  ~(P→Q)→(Q→P).
Proof. intros P Q.
  specialize n2_52 with P Q. 
  intros n2_52a.
  specialize Trans2_17 with Q P. 
  intros Trans2_17a.
  Syll n2_52a Trans2_17a S.
  apply S.
Qed.

Theorem n2_53 : ∀ P Q : Prop,
  (P ∨ Q) → (~P → Q).
Proof. intros P Q.
  specialize n2_12 with P. 
  intros n2_12a.
  specialize n2_38 with Q P (~~P). 
  intros n2_38a.
  MP n2_38a n2_12a.
  replace (~~P∨Q) with (~P→Q) in n2_38a.
  apply n2_38a. 
  apply Impl1_01.
Qed.

Theorem n2_54 : ∀ P Q : Prop,
  (~P → Q) → (P ∨ Q).
Proof. intros P Q.
  specialize n2_14 with P. 
  intros n2_14a.
  specialize n2_38 with Q (~~P) P. 
  intros n2_38a.
  MP n2_38a n2_12a.
  replace (~~P∨Q) with (~P→Q) in n2_38a.
  apply n2_38a. 
  apply Impl1_01.
Qed.

Theorem n2_55 : ∀ P Q : Prop,
  ~P → ((P ∨ Q) → Q).
Proof. intros P Q.
  specialize n2_53 with P Q.
  intros n2_53a.
  specialize Comm2_04 with (P∨Q) (~P) Q. 
  intros Comm2_04a.
  MP n2_53a Comm2_04a.
  apply Comm2_04a.
Qed.

Theorem n2_56 : ∀ P Q : Prop,
  ~Q → ((P ∨ Q) → P).
Proof. intros P Q.
  specialize n2_55 with Q P. 
  intros n2_55a.
  specialize Perm1_4 with P Q. 
  intros Perm1_4a.
  specialize Syll2_06 with (P∨Q) (Q∨P) P. 
  intros Syll2_06a.
  MP Syll2_06a Perm1_4a.
Qed. 

Theorem n2_6 : ∀ P Q : Prop,
  (~P→Q) → ((P → Q) → Q).
Proof. intros P Q.
  specialize n2_38 with Q (~P) Q. 
  intros n2_38a.
  specialize Taut1_2 with Q. 
  intros Taut1_2a.
  specialize Syll2_05 with (~P∨Q) (Q∨Q) Q. 
  intros Syll2_05a.
  MP Syll2_05a Taut1_2a.
  Syll n2_38a Syll2_05a S.
  replace (~P∨Q) with (P→Q) in S.
  apply S.
  apply Impl1_01.
Qed.

Theorem n2_61 : ∀ P Q : Prop,
  (P → Q) → ((~P → Q) → Q).
Proof. intros P Q.
  specialize n2_6 with P Q. 
  intros n2_6a.
  specialize Comm2_04 with (~P→Q) (P→Q) Q. 
  intros Comm2_04a.
  MP Comm2_04a n2_6a.
  apply Comm2_04a.
Qed.

Theorem n2_62 : ∀ P Q : Prop,
  (P ∨ Q) → ((P → Q) → Q).
Proof. intros P Q.
  specialize n2_53 with P Q. 
  intros n2_53a.
  specialize n2_6 with P Q. 
  intros n2_6a.
  Syll n2_53a n2_6a S.
  apply S.
Qed.

Theorem n2_621 : ∀ P Q : Prop,
  (P → Q) → ((P ∨ Q) → Q).
Proof. intros P Q.
  specialize n2_62 with P Q. 
  intros n2_62a.
  specialize Comm2_04 with (P ∨ Q) (P→Q) Q. 
  intros Comm2_04a.
  MP Comm2_04a n2_62a. 
  apply Comm2_04a.
Qed.

Theorem n2_63 : ∀ P Q : Prop,
  (P ∨ Q) → ((~P ∨ Q) → Q).
Proof. intros P Q.
  specialize n2_62 with P Q. 
  intros n2_62a.
  replace (~P∨Q) with (P→Q).
  apply n2_62a.
  apply Impl1_01.
Qed.

Theorem n2_64 : ∀ P Q : Prop,
  (P ∨ Q) → ((P ∨ ~Q) → P).
Proof. intros P Q.
  specialize n2_63 with Q P. 
  intros n2_63a.
  specialize Perm1_4 with P Q. 
  intros Perm1_4a.
  Syll n2_63a Perm1_4a Ha.
  specialize Syll2_06 with (P∨~Q) (~Q∨P) P.
  intros Syll2_06a.
  specialize Perm1_4 with P (~Q).
  intros Perm1_4b.
  MP Syll2_05a Perm1_4b.
  Syll Syll2_05a Ha S.
  apply S.
Qed.

Theorem n2_65 : ∀ P Q : Prop,
  (P → Q) → ((P → ~Q) → ~P).
Proof. intros P Q.
  specialize n2_64 with (~P) Q. 
  intros n2_64a.
  replace (~P∨Q) with (P→Q) in n2_64a.
  replace (~P∨~Q) with (P→~Q) in n2_64a.
  apply n2_64a.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n2_67 : ∀ P Q : Prop,
  ((P ∨ Q) → Q) → (P → Q).
Proof. intros P Q.
  specialize n2_54 with P Q. 
  intros n2_54a.
  specialize Syll2_06 with (~P→Q) (P∨Q) Q. 
  intros Syll2_06a.
  MP Syll2_06a n2_54a.
  specialize n2_24 with  P Q. 
  intros n2_24.
  specialize Syll2_06 with P (~P→Q) Q. 
  intros Syll2_06b.
  MP Syll2_06b n2_24a.
  Syll Syll2_06b Syll2_06a S.
  apply S.
Qed.

Theorem n2_68 : ∀ P Q : Prop,
  ((P → Q) → Q) → (P ∨ Q).
Proof. intros P Q.
  specialize n2_67 with (~P) Q. 
  intros n2_67a.
  replace (~P∨Q) with (P→Q) in n2_67a.
  specialize n2_54 with P Q. 
  intros n2_54a.
  Syll n2_67a n2_54a S.
  apply S.
  apply Impl1_01.
Qed.

Theorem n2_69 : ∀ P Q : Prop,
  ((P → Q) → Q) → ((Q → P) → P).
Proof. intros P Q.
  specialize n2_68 with P Q. 
  intros n2_68a.
  specialize Perm1_4 with P Q. 
  intros Perm1_4a.
  Syll n2_68a Perm1_4a Sa.
  specialize n2_62 with Q P. 
  intros n2_62a.
  Syll Sa n2_62a Sb.
  apply Sb.
Qed.

Theorem n2_73 : ∀ P Q R : Prop,
  (P → Q) → (((P ∨ Q) ∨ R) → (Q ∨ R)).
Proof. intros P Q R.
  specialize n2_621 with P Q. 
  intros n2_621a.
  specialize n2_38 with R (P∨Q) Q. 
  intros n2_38a.
  Syll n2_621a n2_38a S.
  apply S.
Qed.

Theorem n2_74 : ∀ P Q R : Prop,
  (Q → P) → ((P ∨ Q) ∨ R) → (P ∨ R).
Proof. intros P Q R.
  specialize n2_73 with Q P R. 
  intros n2_73a.
  specialize Assoc1_5 with P Q R. 
  intros Assoc1_5a.
  specialize n2_31 with Q P R. 
  intros n2_31a. (*not cited explicitly!*)
  Syll Assoc1_5a n2_31a Sa. 
  specialize n2_32 with P Q R. 
  intros n2_32a. (*not cited explicitly!*)
  Syll n2_32a Sa Sb.
  specialize Syll2_06 with ((P∨Q)∨R) ((Q∨P)∨R) (P∨R). 
  intros Syll2_06a.
  MP Syll2_06a Sb.
  Syll n2_73a Syll2_05a H.
  apply H.
Qed.

Theorem n2_75 : ∀ P Q R : Prop,
  (P ∨ Q) → ((P ∨ (Q → R)) → (P ∨ R)).
Proof. intros P Q R.
  specialize n2_74 with P (~Q) R. 
  intros n2_74a.
  specialize n2_53 with Q P. 
  intros n2_53a.
  Syll n2_53a n2_74a Sa.
  specialize n2_31 with P (~Q) R. 
  intros n2_31a.
  specialize Syll2_06 with (P∨(~Q)∨R)((P∨(~Q))∨R)  (P∨R). 
  intros Syll2_06a.
  MP Syll2_06a n2_31a.
  Syll Sa Syll2_06a Sb.
  specialize Perm1_4 with P Q. 
  intros Perm1_4a. (*not cited!*)
  Syll Perm1_4a Sb Sc.
  replace (~Q∨R) with (Q→R) in Sc.
  apply Sc.
  apply Impl1_01.
Qed.

Theorem n2_76 : ∀ P Q R : Prop,
  (P ∨ (Q → R)) → ((P ∨ Q) → (P ∨ R)).
Proof. intros P Q R.
  specialize n2_75 with P Q R. 
  intros n2_75a.
  specialize Comm2_04 with (P∨Q) (P∨(Q→R)) (P∨R). 
  intros Comm2_04a.
  apply Comm2_04a.
  apply n2_75a. 
Qed.

Theorem n2_77 : ∀ P Q R : Prop,
  (P → (Q → R)) → ((P → Q) → (P → R)).
Proof. intros P Q R.
  specialize n2_76 with (~P) Q R. 
  intros n2_76a.
  replace (~P∨(Q→R)) with (P→Q→R) in n2_76a.
  replace (~P∨Q) with (P→Q) in n2_76a.
  replace (~P∨R) with (P→R) in n2_76a.
  apply n2_76a.
  apply Impl1_01. 
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n2_8 : ∀ Q R S : Prop,
  (Q ∨ R) → ((~R ∨ S) → (Q ∨ S)).
Proof. intros Q R S.
  specialize n2_53 with R Q. 
  intros n2_53a.
  specialize Perm1_4 with Q R. 
  intros Perm1_4a.
  Syll Perm1_4a n2_53a Ha.
  specialize n2_38 with S (~R) Q. 
  intros n2_38a.
  Syll H n2_38a Hb.
  apply Hb.
Qed.

Theorem n2_81 : ∀ P Q R S : Prop,
  (Q → (R → S)) → ((P ∨ Q) → ((P ∨ R) → (P ∨ S))).
Proof. intros P Q R S.
  specialize Sum1_6 with P Q (R→S). 
  intros Sum1_6a.
  specialize n2_76 with P R S. 
  intros n2_76a.
  specialize Syll2_05 with (P∨Q) (P∨(R→S)) ((P∨R)→(P∨S)). 
  intros Syll2_05a.
  MP Syll2_05a n2_76a.
  Syll Sum1_6a Syll2_05a H.
  apply H.
Qed.

Theorem n2_82 : ∀ P Q R S : Prop,
  (P ∨ Q ∨ R)→((P ∨ ~R ∨ S)→(P ∨ Q ∨ S)).
Proof. intros P Q R S.
  specialize n2_8 with Q R S. 
  intros n2_8a.
  specialize n2_81 with P (Q∨R) (~R∨S) (Q∨S). 
  intros n2_81a.
  MP n2_81a n2_8a.
  apply n2_81a.
Qed.

Theorem n2_83 : ∀ P Q R S : Prop,
  (P→(Q→R))→((P→(R→S))→(P→(Q→S))).
Proof. intros P Q R S.
  specialize n2_82 with (~P) (~Q) R S. 
  intros n2_82a.
  replace (~Q∨R) with (Q→R) in n2_82a.
  replace (~P∨(Q→R)) with (P→Q→R) in n2_82a.
  replace (~R∨S) with (R→S) in n2_82a.
  replace (~P∨(R→S)) with (P→R→S) in n2_82a.
  replace (~Q∨S) with (Q→S) in n2_82a.
  replace (~Q∨S) with (Q→S) in n2_82a.
  replace (~P∨(Q→S)) with (P→Q→S) in n2_82a.
  apply n2_82a.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
Qed.

Theorem n2_85 : ∀ P Q R : Prop,
  ((P ∨ Q) → (P ∨ R)) → (P ∨ (Q → R)).
Proof. intros P Q R.
  specialize Add1_3 with P Q. 
  intros Add1_3a.
  specialize Syll2_06 with Q (P∨Q) R. 
  intros Syll2_06a.
  MP Syll2_06a Add1_3a.
  specialize n2_55 with P R. 
  intros n2_55a.
  specialize Syll2_05 with (P∨Q) (P∨R) R. 
  intros Syll2_05a.
  Syll n2_55a Syll2_05a Ha.
  specialize n2_83 with (~P) ((P∨Q)→(P∨R)) ((P∨Q)→R) (Q→R). 
  intros n2_83a.
  MP n2_83a Ha.
  specialize Comm2_04 with (~P) (P∨Q→P∨R) (Q→R). 
  intros Comm2_04a.
  Syll Ha Comm2_04a Hb.
  specialize n2_54 with P (Q→R). 
  intros n2_54a.
  specialize n2_02 with (~P) ((P∨Q→R)→(Q→R)). 
  intros n2_02a. (*Not mentioned! Greg's suggestion per the BRS list in June 25, 2017.*)
  MP Syll2_06a n2_02a.
  MP Hb n2_02a.
  Syll Hb n2_54a Hc.
  apply Hc.
Qed.

Theorem n2_86 : ∀ P Q R : Prop,
  ((P → Q) → (P → R)) → (P → (Q →  R)).
Proof. intros P Q R.
  specialize n2_85 with (~P) Q R. 
  intros n2_85a.
  replace (~P∨Q) with (P→Q) in n2_85a.
  replace (~P∨R) with (P→R) in n2_85a.
  replace (~P∨(Q→R)) with (P→Q→R) in n2_85a.
  apply n2_85a.
  apply Impl1_01. 
  apply Impl1_01. 
  apply Impl1_01.
Qed.

End No2.

Module No3.

Import No1.
Import No2.
 
Axiom Prod3_01 : ∀ P Q : Prop, 
  (P ∧ Q) = ~(~P ∨ ~Q).

Axiom Abb3_02 : ∀ P Q R : Prop, 
  (P→Q→R)=(P→Q)∧(Q→R).

Theorem Conj3_03 : ∀ P Q : Prop, P → Q → (P∧Q). (*3.03 is a derived rule permitting an inference from the theoremhood of P and that of Q to that of P and Q.*)
Proof. intros P Q.
  specialize n2_11 with (~P∨~Q). intros n2_11a.
  specialize n2_32 with (~P) (~Q) (~(~P ∨ ~Q)). intros n2_32a.
  MP n2_32a n2_11a.
  replace (~(~P∨~Q)) with (P∧Q) in n2_32a.
  replace (~Q ∨ (P∧Q)) with (Q→(P∧Q)) in n2_32a.
  replace (~P ∨ (Q → (P∧Q))) with (P→Q→(P∧Q)) in n2_32a.
  apply n2_32a.
  apply Impl1_01.
  apply Impl1_01.
  apply Prod3_01.
Qed.

Theorem n3_1 : ∀ P Q : Prop,
  (P ∧ Q) → ~(~P ∨ ~Q).
Proof. intros P Q.
  replace (~(~P∨~Q)) with (P∧Q).
  specialize n2_08 with (P∧Q). 
  intros n2_08a.
  apply n2_08a.
  apply Prod3_01.
Qed.

Theorem n3_11 : ∀ P Q : Prop,
  ~(~P ∨ ~Q) → (P ∧ Q).
Proof. intros P Q.
  replace (~(~P∨~Q)) with (P∧Q).
  specialize n2_08 with (P∧Q). 
  intros n2_08a.
  apply n2_08a.
  apply Prod3_01.
Qed.

Theorem n3_12 : ∀ P Q : Prop,
  (~P ∨ ~Q) ∨ (P ∧ Q).
Proof. intros P Q.
  specialize n2_11 with (~P∨~Q). 
  intros n2_11a.
  replace (~(~P∨~Q)) with (P∧Q) in n2_11a.
  apply n2_11a.
  apply Prod3_01.
Qed.

Theorem n3_13 : ∀ P Q : Prop,
  ~(P ∧ Q) → (~P ∨ ~Q).
Proof. intros P Q.
  specialize n3_11 with P Q. 
  intros n3_11a.
  specialize Trans2_15 with (~P∨~Q) (P∧Q). 
  intros Trans2_15a.
  MP Trans2_16a n3_11a.
  apply Trans2_15a.
Qed.

Theorem n3_14 : ∀ P Q : Prop,
  (~P ∨ ~Q) → ~(P ∧ Q).
Proof. intros P Q.
  specialize n3_1 with P Q. 
  intros n3_1a.
  specialize Trans2_16 with (P∧Q) (~(~P∨~Q)). 
  intros Trans2_16a.
  MP Trans2_16a n3_1a.
  specialize n2_12 with (~P∨~Q). 
  intros n2_12a.
  Syll n2_12a Trans2_16a S.
  apply S.
Qed.

Theorem n3_2 : ∀ P Q : Prop,
  P → Q → (P ∧ Q).
Proof. intros P Q.
  specialize n3_12 with P Q. 
  intros n3_12a.
  specialize n2_32 with (~P) (~Q) (P∧Q). 
  intros n2_32a.
  MP n3_32a n3_12a.
  replace (~Q ∨ P ∧ Q) with (Q→P∧Q) in n2_32a.
  replace (~P ∨ (Q → P ∧ Q)) with (P→Q→P∧Q) in n2_32a.
  apply n2_32a.
  apply Impl1_01. 
  apply Impl1_01.
Qed.

Theorem n3_21 : ∀ P Q : Prop,
  Q → P → (P ∧ Q).
Proof. intros P Q.
  specialize n3_2 with P Q.
  intros n3_2a.
  specialize Comm2_04 with P Q (P∧Q). 
  intros Comm2_04a.
  MP Comm2_04a n3_2a.
  apply Comm2_04a.
Qed.

Theorem n3_22 : ∀ P Q : Prop,
  (P ∧ Q) → (Q ∧ P).
Proof. intros P Q.
  specialize n3_13 with Q P. 
  intros n3_13a.
  specialize Perm1_4 with (~Q) (~P). 
  intros Perm1_4a.
  Syll n3_13a Perm1_4a Ha.
  specialize n3_14 with P Q. 
  intros n3_14a.
  Syll Ha n3_14a Hb.
  specialize Trans2_17 with (P∧Q) (Q ∧ P). 
  intros Trans2_17a.
  MP Trans2_17a Hb.
  apply Trans2_17a.
Qed.

Theorem n3_24 : ∀ P : Prop,
  ~(P ∧ ~P).
Proof. intros P.
  specialize n2_11 with (~P). 
  intros n2_11a.
  specialize n3_14 with P (~P). 
  intros n3_14a.
  MP n3_14a n2_11a.
  apply n3_14a.
Qed.

Theorem Simp3_26 : ∀ P Q : Prop,
  (P ∧ Q) → P.
Proof. intros P Q.
  specialize n2_02 with Q P. 
  intros n2_02a.
  replace (P→(Q→P)) with (~P∨(Q→P)) in n2_02a.
  replace (Q→P) with (~Q∨P) in n2_02a.
  specialize n2_31 with (~P) (~Q) P. 
  intros n2_31a.
  MP n2_31a n2_02a.
  specialize n2_53 with (~P∨~Q) P. 
  intros n2_53a.
  MP n2_53a n2_02a.
  replace (~(~P∨~Q)) with (P∧Q) in n2_53a.
  apply n2_53a.
  apply Prod3_01.
  replace (~Q∨P) with (Q→P).
  reflexivity.
  apply Impl1_01.
  replace (~P∨(Q→P)) with (P→Q→P).
  reflexivity.
  apply Impl1_01.
Qed.

Theorem Simp3_27 : ∀ P Q : Prop,
  (P ∧ Q) → Q.
Proof. intros P Q.
  specialize n3_22 with P Q. 
  intros n3_22a.
  specialize Simp3_26 with Q P. 
  intros Simp3_26a.
  Syll n3_22a Simp3_26a S.
  apply S.
Qed.

Theorem Exp3_3 : ∀ P Q R : Prop,
  ((P ∧ Q) → R) → (P → (Q → R)).
Proof. intros P Q R.
  specialize Trans2_15 with (~P∨~Q) R. 
  intros Trans2_15a.
  replace (~R→(~P∨~Q)) with (~R→(P→~Q)) in Trans2_15a.
  specialize Comm2_04 with (~R) P (~Q). 
  intros Comm2_04a.
  Syll Trans2_15a Comm2_04a Sa.
  specialize Trans2_17 with Q R. 
  intros Trans2_17a.
  specialize  Syll2_05 with P (~R→~Q) (Q→R). 
  intros Syll2_05a.
  MP Syll2_05a Trans2_17a.
  Syll Sa Syll2_05a Sb.
  replace (~(~P∨~Q)) with (P∧Q) in Sb.
  apply Sb.
  apply Prod3_01.
  replace (~P∨~Q) with (P→~Q).
  reflexivity.
  apply Impl1_01.
Qed.

Theorem Imp3_31 : ∀ P Q R : Prop,
  (P → (Q → R)) → (P ∧ Q) → R.
Proof. intros P Q R.
  specialize n2_31 with (~P) (~Q) R. 
  intros n2_31a.
  specialize n2_53 with (~P∨~Q) R. 
  intros n2_53a.
  Syll n2_31a n2_53a S.
  replace (~Q∨R) with (Q→R) in S.
  replace (~P∨(Q→R)) with (P→Q→R) in S.
  replace (~(~P∨~Q)) with (P∧Q) in S.
  apply S.
  apply Prod3_01.
  apply Impl1_01.
  apply Impl1_01.
Qed.

Theorem Syll3_33 : ∀ P Q R : Prop,
  ((P → Q) ∧ (Q → R)) → (P → R).
Proof. intros P Q R.
  specialize Syll2_06 with P Q R. 
  intros Syll2_06a.
  specialize Imp3_31 with (P→Q) (Q→R) (P→R). 
  intros Imp3_31a.
  MP Imp3_31a Syll2_06a.
  apply Imp3_31a.
Qed.

Theorem Syll3_34 : ∀ P Q R : Prop,
  ((Q → R) ∧ (P → Q)) → (P → R).
Proof. intros P Q R.
  specialize Syll2_05 with P Q R. 
  intros Syll2_05a.
  specialize Imp3_31 with (Q→R) (P→Q) (P→R).
  intros Imp3_31a.
  MP Imp3_31a Syll2_05a.
  apply Imp3_31a.
Qed.

Theorem Ass3_35 : ∀ P Q : Prop,
  (P ∧ (P → Q)) → Q.
Proof. intros P Q.
  specialize n2_27 with P Q. 
  intros n2_27a.
  specialize Imp3_31 with P (P→Q) Q. 
  intros Imp3_31a.
  MP Imp3_31a n2_27a.
  apply Imp3_31a.
Qed.

Theorem n3_37 : ∀ P Q R : Prop,
  (P ∧ Q → R) → (P ∧ ~R → ~Q).
Proof. intros P Q R.
  specialize Trans2_16 with Q R. 
  intros Trans2_16a.
  specialize Syll2_05 with P (Q→R) (~R→~Q). 
  intros Syll2_05a.
  MP Syll2_05a Trans2_16a.
  specialize Exp3_3 with P Q R. 
  intros Exp3_3a.
  Syll Exp3_3a Syll2_05a Sa.
  specialize Imp3_31 with P (~R) (~Q). 
  intros Imp3_31a.
  Syll Sa Imp3_31a Sb.
  apply Sb.
Qed.

Theorem n3_4 : ∀ P Q : Prop,
  (P ∧ Q) → P → Q.
Proof. intros P Q.
  specialize n2_51 with P Q. 
  intros n2_51a.
  specialize Trans2_15 with (P→Q) (P→~Q). 
  intros Trans2_15a.
  MP Trans2_15a n2_51a.
  replace (P→~Q) with (~P∨~Q) in Trans2_15a.
  replace (~(~P∨~Q)) with (P∧Q) in Trans2_15a.
  apply Trans2_15a.
  apply Prod3_01.
  replace (~P∨~Q) with (P→~Q).
  reflexivity.
  apply Impl1_01.
Qed.

Theorem n3_41 : ∀ P Q R : Prop,
  (P → R) → (P ∧ Q → R).
Proof. intros P Q R.
  specialize Simp3_26 with P Q. 
  intros Simp3_26a.
  specialize Syll2_06 with (P∧Q) P R. 
  intros Syll2_06a.
  MP Simp3_26a Syll2_06a.
  apply Syll2_06a.
Qed.

Theorem n3_42 : ∀ P Q R : Prop,
  (Q → R) → (P ∧ Q → R).
Proof. intros P Q R.
  specialize Simp3_27 with P Q. 
  intros Simp3_27a.
  specialize Syll2_06 with (P∧Q) Q R. 
  intros Syll2_06a.
  MP Syll2_05a Simp3_27a.
  apply Syll2_06a.
Qed.

Theorem Comp3_43 : ∀ P Q R : Prop,
  (P → Q) ∧ (P → R) → (P → Q ∧ R).
Proof. intros P Q R.
  specialize n3_2 with Q R. 
  intros n3_2a.
  specialize Syll2_05 with P Q (R→Q∧R). 
  intros Syll2_05a.
  MP Syll2_05a n3_2a.
  specialize n2_77 with P R (Q∧R). 
  intros n2_77a.
  Syll Syll2_05a n2_77a Sa.
  specialize Imp3_31 with (P→Q) (P→R) (P→Q∧R). 
  intros Imp3_31a.
  MP Sa Imp3_31a.
  apply Imp3_31a.
Qed.

Theorem n3_44 : ∀ P Q R : Prop,
  (Q → P) ∧ (R → P) → (Q ∨ R → P).
Proof. intros P Q R.
  specialize Syll3_33 with (~Q) R P. 
  intros Syll3_33a.
  specialize n2_6 with Q P. 
  intros n2_6a.
  Syll Syll3_33a n2_6a Sa.
  specialize Exp3_3 with (~Q→R) (R→P) ((Q→P)→P). 
  intros Exp3_3a.
  MP Exp3_3a Sa.
  specialize Comm2_04 with (R→P) (Q→P) P. 
  intros Comm2_04a.
  Syll Exp3_3a Comm2_04a Sb.
  specialize Imp3_31 with (Q→P) (R→P) P. 
  intros Imp3_31a.
  Syll Sb Imp3_31a Sc.
  specialize Comm2_04 with (~Q→R) ((Q→P)∧(R→P)) P. 
  intros Comm2_04b.
  MP Comm2_04b Sc.
  specialize n2_53 with Q R. 
  intros n2_53a.
  specialize Syll2_06 with (Q∨R) (~Q→R) P. 
  intros Syll2_06a.
  MP Syll2_06a n2_53a.
  Syll Comm2_04b Syll2_06a Sd.
  apply Sd.
Qed.

Theorem Fact3_45 : ∀ P Q R : Prop,
  (P → Q) → (P ∧ R) → (Q ∧ R).
Proof. intros P Q R.
  specialize Syll2_06 with P Q (~R). 
  intros Syll2_06a.
  specialize Trans2_16 with (Q→~R) (P→~R). 
  intros Trans2_16a.
  Syll Syll2_06a Trans2_16a S.
  replace (P→~R) with (~P∨~R) in S.
  replace (Q→~R) with (~Q∨~R) in S.
  replace (~(~P∨~R)) with (P∧R) in S.
  replace (~(~Q∨~R)) with (Q∧R) in S.
  apply S.
  apply Prod3_01.
  apply Prod3_01.
  replace (~Q∨~R) with (Q→~R).
  reflexivity.
  apply Impl1_01.
  replace (~P∨~R) with (P→~R).
  reflexivity.
  apply Impl1_01.
Qed.

Theorem n3_47 : ∀ P Q R S : Prop,
  ((P → R) ∧ (Q → S)) → (P ∧ Q) → R ∧ S.
Proof. intros P Q R S.
  specialize Simp3_26 with (P→R) (Q→S). 
  intros Simp3_26a.
  specialize Fact3_45 with P R Q. 
  intros Fact3_45a.
  Syll Simp3_26a Fact3_45a Sa.
  specialize n3_22 with R Q. 
  intros n3_22a.
  specialize Syll2_05 with (P∧Q) (R∧Q) (Q∧R). 
  intros Syll2_05a.
  MP Syll2_05a n3_22a.
  Syll Sa Syll2_05a Sb.
  specialize Simp3_27 with (P→R) (Q→S).
  intros Simp3_27a.
  specialize Fact3_45 with Q S R. 
  intros Fact3_45b.
  Syll Simp3_27a Fact3_45b Sc.
  specialize n3_22 with S R. 
  intros n3_22b.
  specialize Syll2_05 with (Q∧R) (S∧R) (R∧S). 
  intros Syll2_05b.
  MP Syll2_05b n3_22b.
  Syll Sc Syll2_05b Sd.
  specialize n2_83 with ((P→R)∧(Q→S)) (P∧Q) (Q∧R) (R∧S).
  intros n2_83a.
  MP n2_83a Sb.
  MP n2_83 Sd.
  apply n2_83a.
Qed.

Theorem n3_48 : ∀ P Q R S : Prop,
  ((P → R) ∧ (Q → S)) → (P ∨ Q) → R ∨ S.
Proof. intros P Q R S.
  specialize Simp3_26 with (P→R) (Q→S). 
  intros Simp3_26a.
  specialize Sum1_6 with Q P R. 
  intros Sum1_6a.
  Syll Simp3_26a Sum1_6a Sa.
  specialize Perm1_4 with P Q. 
  intros Perm1_4a.
  specialize Syll2_06 with (P∨Q) (Q∨P) (Q∨R). 
  intros Syll2_06a.
  MP Syll2_06a Perm1_4a.
  Syll Sa Syll2_06a Sb.
  specialize Simp3_27 with (P→R) (Q→S). 
  intros Simp3_27a.
  specialize Sum1_6 with R Q S. 
  intros Sum1_6b.
  Syll Simp3_27a Sum1_6b Sc.
  specialize Perm1_4 with Q R. 
  intros Perm1_4b.
  specialize Syll2_06 with (Q∨R) (R∨Q) (R∨S). 
  intros Syll2_06b.
  MP Syll2_06b Perm1_4b.
  Syll Sc Syll2_06a Sd.
  specialize n2_83 with ((P→R)∧(Q→S)) (P∨Q) (Q∨R) (R∨S). 
  intros n2_83a.
  MP n2_83a Sb.
  MP n2_83a Sd.
  apply n2_83a. 
Qed.

End No3.

Module No4.

Import No1.
Import No2.
Import No3.

Axiom Equiv4_01 : ∀ P Q : Prop, 
  (P↔Q)=((P→Q) ∧ (Q→P)). (*n4_02 defines P iff Q iff R as P iff Q AND Q iff R.*)

Axiom EqBi : ∀ P Q : Prop, 
  (P=Q) ↔ (P↔Q).

Ltac Equiv H1 :=
  match goal with 
    | [ H1 : (?P→?Q) ∧ (?Q→?P) |- _ ] => 
      replace ((P→Q) ∧ (Q→P)) with (P↔Q) in H1
end. 

Ltac Conj H1 H2 :=
  match goal with 
    | [ H1 : ?P, H2 : ?Q |- _ ] => 
      assert (P ∧ Q)
end. 

Theorem Trans4_1 : ∀ P Q : Prop,
  (P → Q) ↔ (~Q → ~P).
Proof. intros P Q.
  specialize Trans2_16 with P Q. 
  intros Trans2_16a.
  specialize Trans2_17 with P Q. 
  intros Trans2_17a.
  Conj Trans2_16a Trans2_17a.
  split. 
  apply Trans2_16a. 
  apply Trans2_17a.
  Equiv H. 
  apply H. 
  apply Equiv4_01.
Qed.

Theorem Trans4_11 : ∀ P Q : Prop,
  (P ↔ Q) ↔ (~P ↔ ~Q).
Proof. intros P Q.
  specialize Trans2_16 with P Q. 
  intros Trans2_16a.
  specialize Trans2_16 with Q P. 
  intros Trans2_16b.
  Conj Trans2_16a Trans2_16b.
  split.
  apply Trans2_16a.
  apply Trans2_16b.
  specialize n3_47 with (P→Q) (Q→P) (~Q→~P) (~P→~Q). 
  intros n3_47a.
  MP n3_47 H.
  specialize n3_22 with (¬ Q → ¬ P) (¬ P → ¬ Q). 
  intros n3_22a.
  Syll n3_47a n3_22a Sa.
  replace ((P → Q) ∧ (Q → P)) with (P↔Q) in Sa.
  replace ((¬ P → ¬ Q) ∧ (¬ Q → ¬ P)) with (~P↔~Q) in Sa.
  clear Trans2_16a. clear H. clear Trans2_16b. clear n3_22a. clear n3_47a.
  specialize Trans2_17 with Q P. 
  intros Trans2_17a.
  specialize Trans2_17 with P Q. 
  intros Trans2_17b.
  Conj Trans2_17a Trans2_17b.
  split. 
  apply Trans2_17a. 
  apply Trans2_17b.
  specialize n3_47 with (~P→~Q) (~Q→~P) (Q→P) (P→Q).
  intros n3_47a.
  MP n3_47a H.
  specialize n3_22 with (Q→P) (P→Q).
  intros n3_22a.
  Syll n3_47a n3_22a Sb.
  clear Trans2_17a. clear Trans2_17b. clear H. clear n3_47a. clear n3_22a.
  replace ((P → Q) ∧ (Q → P)) with (P↔Q) in Sb.
  replace ((¬ P → ¬ Q) ∧ (¬ Q → ¬ P)) with (~P↔~Q) in Sb.
  Conj Sa Sb.
  split.
  apply Sa.
  apply Sb.
  Equiv H.
  apply H.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
Qed.

Theorem n4_12 : ∀ P Q : Prop,
  (P ↔ ~Q) ↔ (Q ↔ ~P).
  Proof. intros P Q.
    specialize n2_03 with P Q. 
    intros n2_03a.
    specialize Trans2_15 with Q P. 
    intros Trans2_15a.
    Conj n2_03a Trans2_15a.
    split.
    apply n2_03a.
    apply Trans2_15a.
    specialize n3_47 with (P→~Q) (~Q→P) (Q→~P) (~P→Q).
    intros n3_47a.
    MP n3_47a H.
    specialize n2_03 with Q P. 
    intros n2_03b.
    specialize Trans2_15 with P Q. 
    intros Trans2_15b.
    Conj n2_03b Trans2_15b.
    split.
    apply n2_03b.
    apply Trans2_15b.
    specialize n3_47 with (Q→~P) (~P→Q) (P→~Q) (~Q→P).
    intros n3_47b.
    MP n3_47b H0.
    clear n2_03a. clear Trans2_15a. clear H. clear n2_03b. clear Trans2_15b. clear H0.
    replace ((P → ¬ Q) ∧ (~Q → P)) with (P↔~Q) in n3_47a.
    replace ((Q → ~P) ∧ (~P → Q)) with (Q↔~P) in n3_47a.
    replace ((P → ¬ Q) ∧ (~Q → P)) with (P↔~Q) in n3_47b.
    replace ((Q → ~P) ∧ (~P → Q)) with (Q↔~P) in n3_47b.
    Conj n3_47a n3_47b.
    split.
    apply n3_47a.
    apply n3_47b.
    Equiv H.
    apply H.
    apply Equiv4_01.
    apply Equiv4_01.
    apply Equiv4_01.
    apply Equiv4_01.
    apply Equiv4_01.
  Qed.

Theorem n4_13 : ∀ P : Prop,
  P ↔ ~~P.
  Proof. intros P.
  specialize n2_12 with P. 
  intros n2_12a.
  specialize n2_14 with P. 
  intros n2_14a.
  Conj n2_12a n2_14a.
  split. 
  apply n2_12a. 
  apply n2_14a.
  Equiv H. 
  apply H. 
  apply Equiv4_01.
  Qed.

Theorem n4_14 : ∀ P Q R : Prop,
  ((P ∧ Q) → R) ↔ ((P ∧ ~R) → ~Q).
Proof. intros P Q R.
specialize n3_37 with P Q R. 
intros n3_37a.
specialize n3_37 with P (~R) (~Q).
intros n3_37b.
Conj n3_37a n3_37b.
split. apply n3_37a. 
apply n3_37b.
specialize n4_13 with Q. 
intros n4_13a.
specialize n4_13 with R. 
intros n4_13b.
replace (~~Q) with Q in H.
replace (~~R) with R in H.
Equiv H. 
apply H.
apply Equiv4_01.
apply EqBi. 
apply n4_13b.
apply EqBi. 
apply n4_13a.
Qed.

Theorem n4_15 : ∀ P Q R : Prop,
  ((P ∧ Q) → ~R) ↔ ((Q ∧ R) → ~P).
  Proof. intros P Q R.
  specialize n4_14 with Q P (~R). 
  intros n4_14a.
  specialize n3_22 with Q P. 
  intros n3_22a.
  specialize Syll2_06 with (Q∧P) (P∧Q) (~R). 
  intros Syll2_06a.
  MP Syll2_06a n3_22a.
  specialize n4_13 with R. 
  intros n4_13a.
  replace (~~R) with R in n4_14a.
  rewrite Equiv4_01 in n4_14a.
  specialize Simp3_26 with ((Q ∧ P → ¬ R) → Q ∧ R → ¬ P) ((Q ∧ R → ¬ P) → Q ∧ P → ¬ R). 
  intros Simp3_26a.
  MP Simp3_26a n4_14a.
  Syll Syll2_06a Simp3_26a Sa.
  specialize Simp3_27 with ((Q ∧ P → ¬ R) → Q ∧ R → ¬ P) ((Q ∧ R → ¬ P) → Q ∧ P → ¬ R). 
  intros Simp3_27a.
  MP Simp3_27a n4_14a.
  specialize n3_22 with P Q. 
  intros n3_22b.
  specialize Syll2_06 with (P∧Q) (Q∧P) (~R). 
  intros Syll2_06b.
  MP Syll2_06b n3_22b.
  Syll Syll2_06b Simp3_27a Sb.
  split. 
  apply Sa.
  apply Sb.
  apply EqBi.
  apply n4_13a.
  Qed.

Theorem n4_2 : ∀ P : Prop,
  P ↔ P.
  Proof. intros P.
  specialize n3_2 with (P→P) (P→P). 
  intros n3_2a.
  specialize n2_08 with P. 
  intros n2_08a.
  MP n3_2a n2_08a.
  MP n3_2a n2_08a.
  Equiv n3_2a.
  apply n3_2a.
  apply Equiv4_01.
  Qed.

Theorem n4_21 : ∀ P Q : Prop,
  (P ↔ Q) ↔ (Q ↔ P).
  Proof. intros P Q.
  specialize n3_22 with (P→Q) (Q→P). 
  intros n3_22a.
  specialize Equiv4_01 with P Q. 
  intros Equiv4_01a.
  replace ((P → Q) ∧ (Q → P)) with (P↔Q) in n3_22a.
  specialize Equiv4_01 with Q P. 
  intros Equiv4_01b.
  replace ((Q → P) ∧ (P → Q)) with (Q↔P) in n3_22a.
  specialize n3_22 with (Q→P) (P→Q). 
  intros n3_22b.
  replace ((P → Q) ∧ (Q → P)) with (P↔Q) in n3_22b.
  replace ((Q → P) ∧ (P → Q)) with (Q↔P) in n3_22b.
  Conj n3_22a n3_22b.
  split. 
  apply Equiv4_01b.
  apply n3_22b.
  split. 
  apply n3_22a.
  apply n3_22b.
Qed.

Theorem n4_22 : ∀ P Q R : Prop,
  ((P ↔ Q) ∧ (Q ↔ R)) → (P ↔ R).
Proof. intros P Q R.
  specialize Simp3_26 with (P↔Q) (Q↔R). 
  intros Simp3_26a.
  specialize Simp3_26 with (P→Q) (Q→P). 
  intros Simp3_26b.
  replace ((P→Q) ∧ (Q→P)) with (P↔Q) in Simp3_26b.
  Syll Simp3_26a Simp3_26b Sa.
  specialize Simp3_27 with (P↔Q) (Q↔R). 
  intros Simp3_27a.
  specialize Simp3_26 with (Q→R) (R→Q). 
  intros Simp3_26c.
  replace ((Q→R) ∧ (R→Q)) with (Q↔R) in Simp3_26c.
  Syll Simp3_27a Simp3_26c Sb.
  specialize n2_83 with ((P↔Q)∧(Q↔R)) P Q R. 
  intros n2_83a.
  MP n2_83a Sa. 
  MP n2_83a Sb.
  specialize Simp3_27 with (P↔Q) (Q↔R). 
  intros Simp3_27b.
  specialize Simp3_27 with (Q→R) (R→Q). 
  intros Simp3_27c.
  replace ((Q→R) ∧ (R→Q)) with (Q↔R) in Simp3_27c.
  Syll Simp3_27b Simp3_27c Sc.
  specialize Simp3_26 with (P↔Q) (Q↔R).
  intros Simp3_26d.
  specialize Simp3_27 with (P→Q) (Q→P). 
  intros Simp3_27d.
  replace ((P→Q) ∧ (Q→P)) with (P↔Q) in Simp3_27d.
  Syll Simp3_26d Simp3_27d Sd.
  specialize n2_83 with ((P↔Q)∧(Q↔R)) R Q P. 
  intros n2_83b.
  MP n2_83b Sc. MP n2_83b Sd.
  clear Sd. clear Sb. clear Sc. clear Sa. clear Simp3_26a. clear Simp3_26b. clear Simp3_26c. clear Simp3_26d. clear Simp3_27a. clear Simp3_27b. clear Simp3_27c. clear Simp3_27d.
  Conj n2_83a n2_83b. 
  split.
  apply n2_83a. 
  apply n2_83b.
  specialize Comp3_43 with ((P↔Q)∧(Q↔R)) (P→R) (R→P).
  intros Comp3_43a.
  MP Comp3_43a H.
  replace ((P→R) ∧ (R→P)) with (P↔R) in Comp3_43a.
  apply Comp3_43a.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
Qed.

Theorem n4_24 : ∀ P : Prop,
  P ↔ (P ∧ P).
  Proof. intros P.
  specialize n3_2 with P P. 
  intros n3_2a.
  specialize n2_43 with P (P ∧ P). 
  intros n2_43a.
  MP n3_2a n2_43a.
  specialize Simp3_26 with P P. 
  intros Simp3_26a.
  Conj n2_43a Simp3_26a.
  split.
  apply n2_43a.
  apply Simp3_26a.
  Equiv H.
  apply H.
  apply Equiv4_01.
Qed.

Theorem n4_25 : ∀ P : Prop,
  P ↔ (P ∨ P).
Proof. intros P.
  specialize Add1_3 with P P.
  intros Add1_3a.
  specialize Taut1_2 with P. 
  intros Taut1_2a.
  Conj Add1_3a Taut1_2a.
  split.
  apply Add1_3a.
  apply Taut1_2a.
  Equiv H. apply H.
  apply Equiv4_01.
Qed.

Theorem n4_3 : ∀ P Q : Prop,
  (P ∧ Q) ↔ (Q ∧ P).
Proof. intros P Q.
  specialize n3_22 with P Q.
  intros n3_22a.
  specialize n3_22 with Q P.
  intros n3_22b.
  Conj n3_22a n3_22b.
  split.
  apply n3_22a.
  apply n3_22b.
  Equiv H. apply H.
  apply Equiv4_01.
Qed.

Theorem n4_31 : ∀ P Q : Prop,
  (P ∨ Q) ↔ (Q ∨ P).
  Proof. intros P Q.
    specialize Perm1_4 with P Q.
    intros Perm1_4a.
    specialize Perm1_4 with Q P.
    intros Perm1_4b.
    Conj Perm1_4a Perm1_4b.
    split.
    apply Perm1_4a.
    apply Perm1_4b.
    Equiv H. apply H.
    apply Equiv4_01.
Qed.

  Theorem n4_32 : ∀ P Q R : Prop,
    ((P ∧ Q) ∧ R) ↔ (P ∧ (Q ∧ R)).
    Proof. intros P Q R.
    specialize n4_15 with P Q R.
    intros n4_15a.
    specialize Trans4_1 with P (~(Q ∧ R)).
    intros Trans4_1a.
    replace (~~(Q ∧ R)) with (Q ∧ R) in Trans4_1a.
    replace (Q ∧ R→~P) with (P→~(Q ∧ R)) in n4_15a.
    specialize Trans4_11 with (P ∧ Q → ¬ R) (P → ¬ (Q ∧ R)).
    intros Trans4_11a.
    replace ((P ∧ Q → ¬ R) ↔ (P → ¬ (Q ∧ R))) with (¬ (P ∧ Q → ¬ R) ↔ ¬ (P → ¬ (Q ∧ R))) in n4_15a.
    replace (P ∧ Q → ¬ R) with (~(P ∧ Q ) ∨ ¬ R) in n4_15a.
    replace (P → ¬ (Q ∧ R)) with (~P ∨ ~(Q ∧ R)) in n4_15a.
    replace (¬ (¬ (P ∧ Q) ∨ ¬ R)) with ((P ∧ Q) ∧ R) in n4_15a.
    replace (¬ (¬ P ∨ ¬ (Q ∧ R))) with (P ∧ (Q ∧ R )) in n4_15a.
    apply n4_15a.
    apply Prod3_01.
    apply Prod3_01.
    rewrite Impl1_01.
    reflexivity.
    rewrite Impl1_01.
    reflexivity.
    replace (¬ (P ∧ Q → ¬ R) ↔ ¬ (P → ¬ (Q ∧ R))) with ((P ∧ Q → ¬ R) ↔ (P → ¬ (Q ∧ R))).
    reflexivity.
    apply EqBi.
    apply Trans4_11a.
    apply EqBi.
    apply Trans4_1a.
    apply EqBi.
    apply n4_13. 
    Qed. (*Note that the actual proof uses n4_12, but that transposition involves transforming a biconditional into a conditional. This way of doing it - using Trans4_1 to transpose a conditional and then applying n4_13 to double negate - is easier without a derived rule for replacing a biconditional with one of its equivalent implications.*)

Theorem n4_33 : ∀ P Q R : Prop,
  (P ∨ (Q ∨ R)) ↔ ((P ∨ Q) ∨ R).
  Proof. intros P Q R.
    specialize n2_31 with P Q R.
    intros n2_31a.
    specialize n2_32 with P Q R.
    intros n2_32a.
    split. apply n2_31a.
    apply n2_32a.
  Qed.

  Axiom n4_34 : ∀ P Q R : Prop,
  P ∧ Q ∧ R = ((P ∧ Q) ∧ R). (*This axiom ensures left association of brackets. Coq's default is right association. But Principia proves associativity of logical product as n4_32. So in effect, this axiom gives us a derived rule that allows us to shift between Coq's and Principia's default rules for brackets of logical products.*)

Theorem n4_36 : ∀ P Q R : Prop,
  (P ↔ Q) → ((P ∧ R) ↔ (Q ∧ R)).
Proof. intros P Q R.
  specialize Fact3_45 with P Q R.
  intros Fact3_45a.
  specialize Fact3_45 with Q P R.
  intros Fact3_45b.
  Conj Fact3_45a Fact3_45b.
  split.
  apply Fact3_45a.
  apply Fact3_45b.
  specialize n3_47 with (P→Q) (Q→P) (P ∧ R → Q ∧ R) (Q ∧ R → P ∧ R).
  intros n3_47a.
  MP n3_47 H.
  replace  ((P → Q) ∧ (Q → P)) with (P↔Q) in n3_47a.
  replace ((P ∧ R → Q ∧ R) ∧ (Q ∧ R → P ∧ R)) with (P ∧ R ↔ Q ∧ R) in n3_47a.
  apply n3_47a.
  apply Equiv4_01.
  apply Equiv4_01.
  Qed.

Theorem n4_37 : ∀ P Q R : Prop,
  (P ↔ Q) → ((P ∨ R) ↔ (Q ∨ R)).
Proof. intros P Q R.
  specialize Sum1_6 with R P Q.
  intros Sum1_6a.
  specialize Sum1_6 with R Q P.
  intros Sum1_6b.
  Conj Sum1_6a Sum1_6b.
  split.
  apply Sum1_6a.
  apply Sum1_6b.
  specialize n3_47 with (P → Q) (Q → P) (R ∨ P → R ∨ Q) (R ∨ Q → R ∨ P).
  intros n3_47a.
  MP n3_47 H.
  replace  ((P → Q) ∧ (Q → P)) with (P↔Q) in n3_47a.
  replace ((R ∨ P → R ∨ Q) ∧ (R ∨ Q → R ∨ P)) with (R ∨ P ↔ R ∨ Q) in n3_47a.
  replace (R ∨ P) with (P ∨ R) in n3_47a.
  replace (R ∨ Q) with (Q ∨ R) in n3_47a.
  apply n3_47a.
  apply EqBi.
  apply n4_31.
  apply EqBi.
  apply n4_31.
  apply Equiv4_01.
  apply Equiv4_01.
  Qed.

Theorem n4_38 : ∀ P Q R S : Prop,
  ((P ↔ R) ∧ (Q ↔ S)) → ((P ∧ Q) ↔ (R ∧ S)).
Proof. intros P Q R S.
  specialize n3_47 with P Q R S.
  intros n3_47a.
  specialize n3_47 with R S P Q.
  intros n3_47b.
  Conj n3_47a n3_47b.
  split.
  apply n3_47a.
  apply n3_47b.
  specialize n3_47 with ((P→R) ∧ (Q→S)) ((R→P) ∧ (S→Q)) (P ∧ Q → R ∧ S) (R ∧ S → P ∧ Q).
  intros n3_47c.
  MP n3_47c H.
  specialize n4_32 with (P→R) (Q→S) ((R→P) ∧ (S → Q)).
  intros n4_32a.
  replace (((P → R) ∧ (Q → S)) ∧ (R → P) ∧ (S → Q)) with ((P → R) ∧ (Q → S) ∧ (R → P) ∧ (S → Q)) in n3_47c.
  specialize n4_32 with (Q→S) (R→P) (S → Q).
  intros n4_32b.
  replace ((Q → S) ∧ (R → P) ∧ (S → Q)) with (((Q → S) ∧ (R → P)) ∧ (S → Q)) in n3_47c.
  specialize n3_22 with (Q→S) (R→P).
  intros n3_22a.
  specialize n3_22 with (R→P) (Q→S).
  intros n3_22b.
  Conj n3_22a n3_22b.
  split.
  apply n3_22a.
  apply n3_22b.
  Equiv H0.
  replace ((Q → S) ∧ (R → P)) with ((R → P) ∧ (Q → S)) in n3_47c.
  specialize n4_32 with (R → P) (Q → S) (S → Q).
  intros n4_32c.
  replace (((R → P) ∧ (Q → S)) ∧ (S → Q)) with ((R → P) ∧ (Q → S) ∧ (S → Q)) in n3_47c.
  specialize n4_32 with (P→R) (R → P) ((Q → S)∧(S → Q)).
  intros n4_32d.
  replace ((P → R) ∧ (R → P) ∧ (Q → S) ∧ (S → Q)) with (((P → R) ∧ (R → P)) ∧ (Q → S) ∧ (S → Q)) in n3_47c.
  replace ((P→R) ∧ (R → P)) with (P↔R) in n3_47c.
  replace ((Q → S) ∧ (S → Q)) with (Q↔S) in n3_47c.
  replace ((P ∧ Q → R ∧ S) ∧ (R ∧ S → P ∧ Q)) with ((P ∧ Q) ↔ (R ∧ S)) in n3_47c.
  apply n3_47c.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  apply EqBi.
  apply n4_32d.
  replace ((R → P) ∧ (Q → S) ∧ (S → Q)) with (((R → P) ∧ (Q → S)) ∧ (S → Q)).
  reflexivity.
  apply EqBi.
  apply n4_32c.
  replace ((R → P) ∧ (Q → S)) with ((Q → S) ∧ (R → P)).
  reflexivity.
  apply EqBi.
  apply H0.
  apply Equiv4_01.
  apply EqBi.
  apply n4_32b.
  replace ((P → R) ∧ (Q → S) ∧ (R → P) ∧ (S → Q)) with (((P → R) ∧ (Q → S)) ∧ (R → P) ∧ (S → Q)).
  reflexivity.
  apply EqBi.
  apply n4_32a.
  Qed.

Theorem n4_39 : ∀ P Q R S : Prop,
  ((P ↔ R) ∧ (Q ↔ S)) → ((P ∨ Q) ↔ (R ∨ S)).
Proof.  intros P Q R S.
  specialize n3_48 with P Q R S.
  intros n3_48a.
  specialize n3_48 with R S P Q.
  intros n3_48b.
  Conj n3_48a n3_48b.
  split.
  apply n3_48a.
  apply n3_48b.
  specialize n3_47 with ((P → R) ∧ (Q → S)) ((R → P) ∧ (S → Q)) (P ∨ Q → R ∨ S) (R ∨ S → P ∨ Q).
  intros n3_47a.
  MP n3_47a H.
  replace ((P ∨ Q → R ∨ S) ∧ (R ∨ S → P ∨ Q)) with ((P ∨ Q) ↔ (R ∨ S)) in n3_47a.
  specialize n4_32 with ((P → R) ∧ (Q → S)) (R → P) (S → Q).
  intros n4_32a.
  replace (((P → R) ∧ (Q → S)) ∧ (R → P) ∧ (S → Q)) with ((((P → R) ∧ (Q → S)) ∧ (R → P)) ∧ (S → Q)) in n3_47a.
  specialize n4_32 with (P → R) (Q → S) (R → P).
  intros n4_32b.
  replace (((P → R) ∧ (Q → S)) ∧ (R → P)) with ((P → R) ∧ (Q → S) ∧ (R → P)) in n3_47a.
  specialize n3_22 with (Q → S) (R → P).
  intros n3_22a. 
  specialize n3_22 with (R → P) (Q → S).
  intros n3_22b.
  Conj  n3_22a n3_22b.
  split.
  apply n3_22a.
  apply n3_22b.
  Equiv H0.
  replace ((Q → S) ∧ (R → P)) with ((R → P) ∧ (Q → S)) in n3_47a.
  specialize n4_32 with (P → R) (R → P) (Q → S).
  intros n4_32c.
  replace ((P → R) ∧ (R → P) ∧ (Q → S)) with (((P → R) ∧ (R → P)) ∧ (Q → S)) in n3_47a.
  replace ((P → R) ∧ (R → P)) with (P↔R) in n3_47a.
  specialize n4_32 with (P↔R) (Q→S) (S→Q).
  intros n4_32d.
  replace (((P ↔ R) ∧ (Q → S)) ∧ (S → Q)) with ((P ↔ R) ∧ (Q → S) ∧ (S → Q)) in n3_47a.
  replace ((Q → S) ∧ (S → Q)) with (Q ↔ S) in n3_47a.
  apply n3_47a.
  apply Equiv4_01.
  replace ((P ↔ R) ∧ (Q → S) ∧ (S → Q)) with (((P ↔ R) ∧ (Q → S)) ∧ (S → Q)).
  reflexivity.
  apply EqBi.
  apply n4_32d.
  apply Equiv4_01.
  apply EqBi.
  apply n4_32c.
  replace ((R → P) ∧ (Q → S)) with ((Q → S) ∧ (R → P)).
  reflexivity.
  apply EqBi.
  apply H0.
  apply Equiv4_01.
  replace ((P → R) ∧ (Q → S) ∧ (R → P)) with (((P → R) ∧ (Q → S)) ∧ (R → P)).
  reflexivity.
  apply EqBi.
  apply n4_32b.
  apply EqBi.
  apply n4_32a.
  apply Equiv4_01.
  Qed.

Theorem n4_4 : ∀ P Q R : Prop,
  (P ∧ (Q ∨ R)) ↔ ((P∧ Q) ∨ (P ∧ R)).
Proof. intros P Q R.
  specialize n3_2 with P Q.
  intros n3_2a.
  specialize n3_2 with P R.
  intros n3_2b.
  Conj n3_2a n3_2b.
  split.
  apply n3_2a.
  apply n3_2b.
  specialize Comp3_43 with P (Q→P∧Q) (R→P∧R).
  intros Comp3_43a.
  MP Comp3_43a H.
  specialize n3_48 with Q R (P∧Q) (P∧R).
  intros n3_48a.
  Syll Comp3_43a n3_48a Sa.
  specialize Imp3_31 with P (Q∨R) ((P∧ Q) ∨ (P ∧ R)).
  intros Imp3_31a.
  MP Imp3_31a Sa.
  specialize Simp3_26 with P Q.
  intros Simp3_26a.
  specialize Simp3_26 with P R.
  intros Simp3_26b.
  Conj Simp3_26a Simp3_26b.
  split.
  apply Simp3_26a.
  apply Simp3_26b.
  specialize n3_44 with P (P∧Q) (P∧R).
  intros n3_44a.
  MP n3_44a H0.
  specialize Simp3_27 with P Q.
  intros Simp3_27a.
  specialize Simp3_27 with P R.
  intros Simp3_27b.
  Conj Simp3_27a Simp3_27b.
  split.
  apply Simp3_27a.
  apply Simp3_27b.
  specialize n3_48 with (P∧Q) (P∧R) Q R.
  intros n3_48b.
  MP n3_48b H1.
  clear H1. clear Simp3_27a. clear Simp3_27b.
  Conj n3_44a n3_48b.
  split.
  apply n3_44a.
  apply n3_48b.
  specialize Comp3_43 with (P ∧ Q ∨ P ∧ R) P (Q∨R).
  intros Comp3_43b.
  MP Comp3_43b H1.
  clear H1. clear H0. clear n3_44a. clear n3_48b. clear Simp3_26a. clear Simp3_26b.
  Conj Imp3_31a Comp3_43b.
  split.
apply Imp3_31a.
apply Comp3_43b.
Equiv H0.
apply H0.
apply Equiv4_01.
Qed.

Theorem n4_41 : ∀ P Q R : Prop,
  (P ∨ (Q ∧ R)) ↔ ((P ∨ Q) ∧ (P ∨ R)).
Proof. intros P Q R.
  specialize Simp3_26 with Q R.
  intros Simp3_26a.
  specialize Sum1_6 with P (Q ∧ R) Q.
  intros Sum1_6a.
  MP Simp3_26a Sum1_6a.
  specialize Simp3_27 with Q R.
  intros Simp3_27a.
  specialize Sum1_6 with P (Q ∧ R) R.
  intros Sum1_6b.
  MP Simp3_27a Sum1_6b.
  clear Simp3_26a. clear Simp3_27a.
  Conj Sum1_6a Sum1_6b.
  split.
  apply Sum1_6a.
  apply Sum1_6b.
  specialize Comp3_43 with (P ∨ Q ∧ R) (P ∨ Q) (P ∨ R).
  intros Comp3_43a.
  MP Comp3_43a H.
  specialize n2_53 with P Q. 
  intros n2_53a.
  specialize n2_53 with P R. 
  intros n2_53b.
  Conj n2_53a n2_53b.
  split.
  apply n2_53a.
  apply n2_53b.
  specialize n3_47 with (P ∨ Q) (P ∨ R) (¬ P → Q) (¬ P → R).
  intros n3_47a.
  MP n3_47a H0.
  specialize Comp3_43 with (~P) Q R.
  intros Comp3_43b.
  Syll n3_47a Comp3_43b Sa.
  specialize n2_54 with P (Q∧R).
  intros n2_54a.
  Syll Sa n2_54a Sb.
  split.
  apply Comp3_43a.
  apply Sb.
Qed.

Theorem n4_42 : ∀ P Q : Prop,
  P ↔ ((P ∧ Q) ∨ (P ∧ ~Q)).
Proof. intros P Q.
  specialize n3_21 with P (Q ∨ ~Q).
  intros n3_21a.
  specialize n2_11 with Q.
  intros n2_11a.
  MP n3_21a n2_11a.
  specialize Simp3_26 with P (Q ∨ ~Q).
  intros Simp3_26a. clear n2_11a.
  Conj n3_21a Simp3_26a.
  split.
  apply n3_21a.
  apply Simp3_26a.
  Equiv H.
  specialize n4_4 with P Q (~Q).
  intros n4_4a.
  replace (P ∧ (Q ∨ ¬ Q)) with P in n4_4a.
  apply n4_4a.
  apply EqBi.
  apply H.
  apply Equiv4_01.
Qed.

Theorem n4_43 : ∀ P Q : Prop,
  P ↔ ((P ∨ Q) ∧ (P ∨ ~Q)).
Proof. intros P Q.
  specialize n2_2 with P Q.
  intros n2_2a.
  specialize n2_2 with P (~Q).
  intros n2_2b.
  Conj n2_2a n2_2b.
  split.
  apply n2_2a.
  apply n2_2b.
  specialize Comp3_43 with P (P∨Q) (P∨~Q).
  intros Comp3_43a.
  MP Comp3_43a H.
  specialize n2_53 with P Q.
  intros n2_53a.
  specialize n2_53 with P (~Q).
  intros n2_53b.
  Conj n2_53a n2_53b.
  split.
  apply n2_53a.
  apply n2_53b.
  specialize n3_47 with (P∨Q) (P∨~Q) (~P→Q) (~P→~Q).
  intros n3_47a.
  MP n3_47a H0.
  specialize n2_65 with (~P) Q. 
  intros n2_65a.
  replace (~~P) with P in n2_65a.
  specialize Imp3_31 with (¬ P → Q) (¬ P → ¬ Q) (P).
  intros Imp3_31a.
  MP Imp3_31a n2_65a.
  Syll n3_47a Imp3_31a Sa.
  clear n2_2a. clear n2_2b. clear H. clear n2_53a. clear n2_53b. clear H0. clear n2_65a. clear n3_47a. clear Imp3_31a.
  Conj Comp3_43a Sa.
  split.
  apply Comp3_43a.
  apply Sa.
  Equiv H.
  apply H.
  apply Equiv4_01.
  apply EqBi.
  apply n4_13.
Qed.

Theorem n4_44 : ∀ P Q : Prop,
  P ↔ (P ∨ (P ∧ Q)).
  Proof. intros P Q.
    specialize n2_2 with P (P∧Q).
    intros n2_2a.
    specialize n2_08 with P.
    intros n2_08a.
    specialize Simp3_26 with P Q.
    intros Simp3_26a.
    Conj n2_08a Simp3_26a.
    split.
    apply n2_08a.
    apply Simp3_26a.
    specialize n3_44 with P P (P ∧ Q).
    intros n3_44a.
    MP n3_44a H.
    clear H. clear n2_08a. clear Simp3_26a.
    Conj n2_2a n3_44a.
    split.
    apply n2_2a.
    apply n3_44a.
    Equiv H.
    apply H.
    apply Equiv4_01.
  Qed.

Theorem n4_45 : ∀ P Q : Prop,
  P ↔ (P ∧ (P ∨ Q)).
  Proof. intros P Q.
  specialize n2_2 with (P ∧ P) (P ∧ Q).
  intros n2_2a.
  replace (P ∧ P ∨ P ∧ Q) with (P ∧ (P ∨ Q)) in n2_2a.
  replace (P ∧ P) with P in n2_2a.
  specialize Simp3_26 with P (P ∨ Q).
  intros Simp3_26a.
  split.
  apply n2_2a.
  apply Simp3_26a.
  apply EqBi.
  apply n4_24.
  apply EqBi.
  apply n4_4.
Qed.

Theorem n4_5 : ∀ P Q : Prop,
  P ∧ Q ↔ ~(~P ∨ ~Q).
  Proof. intros P Q.
    specialize n4_2 with (P ∧ Q).
    intros n4_2a.
    rewrite Prod3_01.
    replace (~(~P ∨ ~Q)) with (P ∧ Q).
    apply n4_2a.
    apply Prod3_01.
  Qed.

Theorem n4_51 : ∀ P Q : Prop,
  ~(P ∧ Q) ↔ (~P ∨ ~Q).
  Proof. intros P Q.
    specialize n4_5 with P Q.
    intros n4_5a.
    specialize n4_12 with (P ∧ Q) (¬ P ∨ ¬ Q).
    intros n4_12a.
    replace ((P ∧ Q ↔ ¬ (¬ P ∨ ¬ Q)) ↔ (¬ P ∨ ¬ Q ↔ ¬ (P ∧ Q))) with ((P ∧ Q ↔ ¬ (¬ P ∨ ¬ Q)) = (¬ P ∨ ¬ Q ↔ ¬ (P ∧ Q))) in n4_12a.
    replace (P ∧ Q ↔ ¬ (¬ P ∨ ¬ Q)) with (¬ P ∨ ¬ Q ↔ ¬ (P ∧ Q)) in n4_5a.
    replace (¬ P ∨ ¬ Q ↔ ¬ (P ∧ Q)) with (~(P ∧ Q) ↔ (~P ∨ ~Q)) in n4_5a.
    apply n4_5a.
    specialize n4_21 with (¬ (P ∧ Q)) (¬ P ∨ ¬ Q).
    intros n4_21a.
    apply EqBi.
    apply n4_21.
    apply EqBi.
    apply EqBi.
  Qed.

Theorem n4_52 : ∀ P Q : Prop,
  (P ∧ ~Q) ↔ ~(~P ∨ Q).
  Proof. intros P Q.
    specialize n4_5 with P (~Q).
    intros n4_5a.
    replace (~~Q) with Q in n4_5a.
    apply n4_5a.
    specialize n4_13 with Q.
    intros n4_13a.
    apply EqBi.
    apply n4_13a.
  Qed.

Theorem n4_53 : ∀ P Q : Prop,
  ~(P ∧ ~Q) ↔ (~P ∨ Q).
  Proof. intros P Q.
    specialize n4_52 with P Q.
    intros n4_52a.
    specialize n4_12 with ( P ∧ ¬ Q) ((¬ P ∨ Q)).
    intros n4_12a.
    replace ((P ∧ ¬ Q ↔ ¬ (¬ P ∨ Q)) ↔ (¬ P ∨ Q ↔ ¬ (P ∧ ¬ Q))) with ((P ∧ ¬ Q ↔ ¬ (¬ P ∨ Q)) = (¬ P ∨ Q ↔ ¬ (P ∧ ¬ Q))) in n4_12a.
    replace (P ∧ ¬ Q ↔ ¬ (¬ P ∨ Q)) with (¬ P ∨ Q ↔ ¬ (P ∧ ¬ Q)) in n4_52a.
    replace (¬ P ∨ Q ↔ ¬ (P ∧ ¬ Q)) with (~(P ∧ ~Q) ↔ (~P ∨ Q)) in n4_52a.
    apply n4_52a.
    specialize n4_21 with (¬ (P ∧ ¬ Q)) (¬ P ∨ Q).
    intros n4_21a.
    apply EqBi.
    apply n4_21a.
    apply EqBi.
    apply EqBi.
  Qed.

Theorem n4_54 : ∀ P Q : Prop,
  (~P ∧ Q) ↔ ~(P ∨ ~Q).
  Proof. intros P Q.
    specialize n4_5 with (~P) Q.
    intros n4_5a.
    specialize n4_13 with P.
    intros n4_13a.
    replace (~~P) with P in n4_5a.
    apply n4_5a.
    apply EqBi.
    apply n4_13a.
  Qed.

Theorem n4_55 : ∀ P Q : Prop,
  ~(~P ∧ Q) ↔ (P ∨ ~Q).
  Proof. intros P Q.
    specialize n4_54 with P Q.
    intros n4_54a.
    specialize n4_12 with (~P ∧ Q) (P ∨ ~Q).
    intros n4_12a.
    replace (¬ P ∧ Q ↔ ¬ (P ∨ ¬ Q)) with (P ∨ ¬ Q ↔ ¬ (¬ P ∧ Q)) in n4_54a.
    replace (P ∨ ¬ Q ↔ ¬ (¬ P ∧ Q)) with (~(~P ∧ Q) ↔ (P ∨ ~Q)) in n4_54a.
    apply n4_54a.
    specialize n4_21 with (~(~P ∧ Q)) (P ∨ ~Q).
    intros n4_21a.
    apply EqBi.
    apply n4_21a.
    replace ((¬ P ∧ Q ↔ ¬ (P ∨ ¬ Q)) ↔ (P ∨ ¬ Q ↔ ¬ (¬ P ∧ Q))) with ((¬ P ∧ Q ↔ ¬ (P ∨ ¬ Q)) = (P ∨ ¬ Q ↔ ¬ (¬ P ∧ Q))) in n4_12a.
    rewrite n4_12a.
    reflexivity.
    apply EqBi.
    apply EqBi.
  Qed.

Theorem n4_56 : ∀ P Q : Prop,
  (~P ∧ ~Q) ↔ ~(P ∨ Q).
  Proof. intros P Q.
    specialize n4_54 with P (~Q).
    intros n4_54a.
    replace (~~Q) with Q in n4_54a.
    apply n4_54a.
    apply EqBi.
    apply n4_13.
  Qed.

Theorem n4_57 : ∀ P Q : Prop,
  ~(~P ∧ ~Q) ↔ (P ∨ Q).
  Proof. intros P Q.
    specialize n4_56 with P Q.
    intros n4_56a.
    specialize n4_12 with (¬ P ∧ ¬ Q) (P ∨ Q).
    intros n4_12a.
    replace (¬ P ∧ ¬ Q ↔ ¬ (P ∨ Q)) with (P ∨ Q ↔ ¬ (¬ P ∧ ¬ Q)) in n4_56a.
    replace (P ∨ Q ↔ ¬ (¬ P ∧ ¬ Q)) with (¬ (¬ P ∧ ¬ Q) ↔ P ∨ Q) in n4_56a.
    apply n4_56a.
    specialize n4_21 with (¬ (¬ P ∧ ¬ Q)) (P ∨ Q).
    intros n4_21a.
    apply EqBi.
    apply n4_21a.
    replace ((¬ P ∧ ¬ Q ↔ ¬ (P ∨ Q)) ↔ (P ∨ Q ↔ ¬ (¬ P ∧ ¬ Q))) with ((P ∨ Q ↔ ¬ (¬ P ∧ ¬ Q)) ↔ (¬ P ∧ ¬ Q ↔ ¬ (P ∨ Q))) in n4_12a.
    apply EqBi.
    apply n4_12a.
    apply EqBi.
    specialize n4_21 with (P ∨ Q ↔ ¬ (¬ P ∧ ¬ Q)) (¬ P ∧ ¬ Q ↔ ¬ (P ∨ Q)).
    intros n4_21b.
    apply n4_21b.
  Qed.
    
Theorem n4_6 : ∀ P Q : Prop,
  (P → Q) ↔ (~P ∨ Q).
  Proof. intros P Q.
    specialize n4_2 with (~P∨ Q).
    intros n4_2a.
    rewrite Impl1_01.
    apply n4_2a.
  Qed.

Theorem n4_61 : ∀ P Q : Prop,
  ~(P → Q) ↔ (P ∧ ~Q).
  Proof. intros P Q.
  specialize n4_6 with P Q.
  intros n4_6a.
  specialize Trans4_11 with (P→Q) (~P∨Q).
  intros Trans4_11a.
  specialize n4_52 with P Q.
  intros n4_52a.
  replace ((P → Q) ↔ ¬ P ∨ Q) with (¬ (P → Q) ↔ ¬ (¬ P ∨ Q)) in n4_6a.
  replace (¬ (¬ P ∨ Q)) with (P ∧ ¬ Q) in n4_6a.
  apply n4_6a.
  apply EqBi.
  apply n4_52a.
  replace (((P → Q) ↔ ¬ P ∨ Q) ↔ (¬ (P → Q) ↔ ¬ (¬ P ∨ Q))) with ((¬ (P → Q) ↔ ¬ (¬ P ∨ Q)) ↔ ((P → Q) ↔ ¬ P ∨ Q)) in Trans4_11a.
  apply EqBi.
  apply Trans4_11a.
  apply EqBi.
  apply n4_21.
  Qed.

Theorem n4_62 : ∀ P Q : Prop,
  (P → ~Q) ↔ (~P ∨ ~Q).
  Proof. intros P Q.
    specialize n4_6 with P (~Q).
    intros n4_6a.
    apply n4_6a.
  Qed.

Theorem n4_63 : ∀ P Q : Prop,
  ~(P → ~Q) ↔ (P ∧ Q).
  Proof. intros P Q.
    specialize n4_62 with P Q.
    intros n4_62a.
    specialize Trans4_11 with (P → ¬ Q) (¬ P ∨ ¬ Q).
    intros Trans4_11a.
    specialize n4_5 with P Q.
    intros n4_5a.
    replace (¬ (¬ P ∨ ¬ Q)) with (P ∧ Q) in Trans4_11a.
    replace ((P → ¬ Q) ↔ ¬ P ∨ ¬ Q) with ((¬ (P → ¬ Q) ↔ P ∧ Q)) in n4_62a.
    apply n4_62a.
    replace (((P → ¬ Q) ↔ ¬ P ∨ ¬ Q) ↔ (¬ (P → ¬ Q) ↔  P ∧ Q)) with ((¬ (P → ¬ Q) ↔  P ∧ Q) ↔ ((P → ¬ Q) ↔ ¬ P ∨ ¬ Q)) in Trans4_11a.
    apply EqBi.
    apply Trans4_11a.
    specialize n4_21 with (¬ (P → ¬ Q) ↔ P ∧ Q) ((P → ¬ Q) ↔ ¬ P ∨ ¬ Q).
    intros n4_21a.
    apply EqBi.
    apply n4_21a.
    apply EqBi.
    apply n4_5a.
  Qed.

Theorem n4_64 : ∀ P Q : Prop,
  (~P → Q) ↔ (P ∨ Q).
  Proof. intros P Q.
    specialize n2_54 with P Q.
    intros n2_54a.
    specialize n2_53 with P Q.
    intros n2_53a.
    Conj n2_54a n2_53a.
    split.
    apply n2_54a.
    apply n2_53a.
    Equiv H.
    apply H.
    apply Equiv4_01.
  Qed.

Theorem n4_65 : ∀ P Q : Prop,
  ~(~P → Q) ↔ (~P ∧ ~Q).
  Proof. intros P Q.
  specialize n4_64 with P Q.
  intros n4_64a.
  specialize Trans4_11 with(¬ P → Q) (P ∨ Q).
  intros Trans4_11a.
  specialize n4_56 with P Q.
  intros n4_56a.
  replace (((¬ P → Q) ↔ P ∨ Q) ↔ (¬ (¬ P → Q) ↔ ¬ (P ∨ Q))) with ((¬ (¬ P → Q) ↔ ¬ (P ∨ Q)) ↔ ((¬ P → Q) ↔ P ∨ Q)) in Trans4_11a.
  replace ((¬ P → Q) ↔ P ∨ Q) with (¬ (¬ P → Q) ↔ ¬ (P ∨ Q)) in n4_64a.
  replace (¬ (P ∨ Q)) with (¬ P ∧ ¬ Q) in n4_64a.
  apply n4_64a.
  apply EqBi.
  apply n4_56a.
  apply EqBi.
  apply Trans4_11a.
  apply EqBi.
  apply n4_21.
  Qed.

Theorem n4_66 : ∀ P Q : Prop,
  (~P → ~Q) ↔ (P ∨ ~Q).
  Proof. intros P Q.
  specialize n4_64 with P (~Q).
  intros n4_64a.
  apply n4_64a.
  Qed.

Theorem n4_67 : ∀ P Q : Prop,
  ~(~P → ~Q) ↔ (~P ∧ Q).
  Proof. intros P Q.
  specialize n4_66 with P Q.
  intros n4_66a.
  specialize Trans4_11 with (¬ P → ¬ Q) (P ∨ ¬ Q).
  intros Trans4_11a.
  replace ((¬ P → ¬ Q) ↔ P ∨ ¬ Q) with (¬ (¬ P → ¬ Q) ↔ ¬ (P ∨ ¬ Q)) in n4_66a.
  specialize n4_54 with P Q.
  intros n4_54a.
  replace (¬ (P ∨ ¬ Q)) with (¬ P ∧ Q) in n4_66a.
  apply n4_66a.
  apply EqBi.
  apply n4_54a.
  replace (((¬ P → ¬ Q) ↔ P ∨ ¬ Q) ↔ (¬ (¬ P → ¬ Q) ↔ ¬ (P ∨ ¬ Q))) with ((¬ (¬ P → ¬ Q) ↔ ¬ (P ∨ ¬ Q)) ↔ ((¬ P → ¬ Q) ↔ P ∨ ¬ Q)) in Trans4_11a.
  apply EqBi.
  apply Trans4_11a.
  apply EqBi.
  apply n4_21.
  Qed.

Theorem n4_7 : ∀ P Q : Prop,
  (P → Q) ↔ (P → (P ∧ Q)).
  Proof. intros P Q.
  specialize Comp3_43 with P P Q.
  intros Comp3_43a.
  specialize Exp3_3 with  (P → P) (P → Q) (P → P ∧ Q).
  intros Exp3_3a.
  MP Exp3_3a Comp3_43a.
  specialize n2_08 with P.
  intros n2_08a.
  MP Exp3_3a n2_08a.
  specialize Simp3_27 with P Q.
  intros Simp3_27a.
  specialize Syll2_05 with P (P ∧ Q) Q.
  intros Syll2_05a.
  MP Syll2_05a Simp3_26a.
  clear n2_08a. clear Comp3_43a. clear Simp3_27a.
  Conj Syll2_05a Exp3_3a.
  split.
  apply Exp3_3a.
  apply Syll2_05a.
  Equiv H.
  apply H.
  apply Equiv4_01.
  Qed.

Theorem n4_71 : ∀ P Q : Prop,
  (P → Q) ↔ (P ↔ (P ∧ Q)).
  Proof. intros P Q.
  specialize n4_7 with P Q.
  intros n4_7a.
  specialize n3_21 with (P→(P∧Q)) ((P∧Q)→P).
  intros n3_21a.
  replace ((P → P ∧ Q) ∧ (P ∧ Q → P)) with (P↔(P ∧ Q)) in n3_21a.
  specialize Simp3_26 with P Q.
  intros Simp3_26a.
  MP n3_21a Simp3_26a.
  specialize Simp3_26 with (P→(P∧Q)) ((P∧Q)→P).
  intros Simp3_26b.
  replace ((P → P ∧ Q) ∧ (P ∧ Q → P)) with (P↔(P ∧ Q)) in Simp3_26b. clear Simp3_26a.
  Conj n3_21a Simp3_26b.
  split.
  apply n3_21a.
  apply Simp3_26b.
  Equiv H.
  clear n3_21a. clear Simp3_26b.
  Conj n4_7a H.
  split.
  apply n4_7a.
  apply H.
  specialize n4_22 with (P → Q) (P → P ∧ Q) (P ↔ P ∧ Q).
  intros n4_22a.
  MP n4_22a H0.
  apply n4_22a.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  Qed.

Theorem n4_72 : ∀ P Q : Prop,
  (P → Q) ↔ (Q ↔ (P ∨ Q)).
  Proof. intros P Q.
  specialize Trans4_1 with P Q.
  intros Trans4_1a.
  specialize n4_71 with (~Q) (~P).
  intros n4_71a.
  Conj Trans4_1a n4_71a.
  split.
  apply Trans4_1a.
  apply n4_71a.
  specialize n4_22 with (P→Q) (~Q→~P) (~Q↔~Q ∧ ~ P).
  intros n4_22a.
  MP n4_22a H.
  specialize n4_21 with (~Q) (~Q ∧ ~P).
  intros n4_21a.
  Conj n4_22a n4_21a.
  split.
  apply n4_22a.
  apply n4_21a.
  specialize n4_22 with (P→Q) (¬ Q ↔ ¬ Q ∧ ¬ P) (¬ Q ∧ ¬ P ↔ ¬ Q).
  intros n4_22b.
  MP n4_22b H0.
  specialize n4_12 with (~Q ∧ ~ P) (Q).
  intros n4_12a.
  Conj n4_22b n4_12a.
  split.
  apply n4_22b.
  apply n4_12a.
  specialize n4_22 with (P → Q) ((~Q ∧ ~ P) ↔ ~Q) (Q ↔ ~(¬ Q ∧ ¬ P)).
  intros n4_22c.
  MP n4_22b H0.
  specialize n4_57 with Q P.
  intros n4_57a.
  replace (~(~Q ∧ ~P)) with (Q ∨ P) in n4_22c.
  specialize n4_31 with P Q.
  intros n4_31a.
  replace (Q ∨ P) with (P ∨ Q) in n4_22c.
  apply n4_22c.
  apply EqBi.
  apply n4_31a.
  apply EqBi.
  replace (¬ (¬ Q ∧ ¬ P) ↔ Q ∨ P) with (Q ∨ P ↔¬ (¬ Q ∧ ¬ P)) in n4_57a.
  apply n4_57a.
  apply EqBi.
  apply n4_21.
  Qed.

Theorem n4_73 : ∀ P Q : Prop,
  Q → (P ↔ (P ∧ Q)).
  Proof. intros P Q.
  specialize n2_02 with P Q.
  intros n2_02a.
  specialize n4_71 with P Q.
  intros n4_71a.
  replace ((P → Q) ↔ (P ↔ P ∧ Q)) with (((P → Q) → (P ↔ P ∧ Q)) ∧ ((P ↔ P ∧ Q)→(P→Q))) in n4_71a.
  specialize Simp3_26 with ((P → Q) → P ↔ P ∧ Q) (P ↔ P ∧ Q → P → Q).
  intros Simp3_26a.
  MP Simp3_26a n4_71a.
  Syll n2_02a Simp3_26a Sa.
  apply Sa.
  apply Equiv4_01.
  Qed.

Theorem n4_74 : ∀ P Q : Prop,
  ~P → (Q ↔ (P ∨ Q)).
  Proof. intros P Q.
  specialize n2_21 with P Q.
  intros n2_21a.
  specialize n4_72 with P Q.
  intros n4_72a.
  replace (P → Q) with (Q ↔ P ∨ Q) in n2_21a.
  apply n2_21a.
  apply EqBi.
  replace ((P → Q) ↔ (Q ↔ P ∨ Q)) with ((Q ↔ P ∨ Q) ↔ (P → Q)) in n4_72a.
  apply n4_72a.
  apply EqBi.
  apply n4_21.
  Qed.

Theorem n4_76 : ∀ P Q R : Prop,
  ((P → Q) ∧ (P → R)) ↔ (P → (Q ∧ R)).
  Proof. intros P Q R.
  specialize n4_41 with (~P) Q R.
  intros n4_41a.
  replace (~P ∨ Q) with (P→Q) in n4_41a.
  replace (~P ∨ R) with (P→R) in n4_41a.
  replace (¬ P ∨ Q ∧ R) with (P → Q ∧ R) in n4_41a.
  replace ((P → Q ∧ R) ↔ (P → Q) ∧ (P → R)) with ((P → Q) ∧ (P → R) ↔ (P → Q ∧ R)) in n4_41a.
  apply n4_41a.
  apply EqBi.
  apply n4_21.
  apply Impl1_01.
  apply Impl1_01.
  apply Impl1_01.
  Qed.

Theorem n4_77 : ∀ P Q R : Prop,
  ((Q → P) ∧ (R → P)) ↔ ((Q ∨ R) → P).
  Proof. intros P Q R.
  specialize n3_44 with P Q R.
  intros n3_44a.
  split.
  apply n3_44a.
  split.
  specialize n2_2 with Q R.
  intros n2_2a.
  Syll n2_2a H Sa.
  apply Sa.
  specialize Add1_3 with Q R.
  intros Add1_3a.
  Syll Add1_3a H Sb.
  apply Sb.
  Qed. (*Note that we used the split tactic on a conditional, effectively introducing an assumption for conditional proof. It remains to prove that (AvB)→C and A→(AvB) together imply A→C, and similarly that (AvB)→C and B→(AvB) together imply B→C. This can be proved by Syll, but we need a rule of replacement in the context of ((AvB)→C)→(A→C)/\(B→C).*)

Theorem n4_78 : ∀ P Q R : Prop,
  ((P → Q) ∨ (P → R)) ↔ (P → (Q ∨ R)).
  Proof. intros P Q R.
  specialize n4_2 with ((P→Q) ∨ (P → R)).
  intros n4_2a.
  replace (((P → Q) ∨ (P → R))↔((P → Q) ∨ (P → R))) with (((P → Q) ∨ (P → R))↔((¬ P ∨ Q) ∨ ¬ P ∨ R)) in n4_2a.
  specialize n4_33 with (~P) Q (~P ∨ R).
  intros n4_33a.
  replace ((¬ P ∨ Q) ∨ ¬ P ∨ R) with (¬ P ∨ Q ∨ ¬ P ∨ R) in n4_2a.
  specialize n4_31 with (~P) Q.
  intros n4_31a.
  specialize n4_37 with (~P∨Q) (Q ∨ ~P) R.
  intros n4_37a.
  MP n4_37a n4_31a.
  replace (Q ∨ ¬ P ∨ R) with ((Q ∨ ¬ P) ∨ R) in n4_2a.
  replace ((Q ∨ ¬ P) ∨ R) with ((¬ P ∨ Q) ∨ R) in n4_2a.
  specialize n4_33 with (~P) (~P∨Q) R.
  intros n4_33b.
  replace (¬ P ∨ (¬ P ∨ Q) ∨ R) with ((¬ P ∨ (¬ P ∨ Q)) ∨ R) in n4_2a.
  specialize n4_25 with (~P).
  intros n4_25a.
  specialize n4_37 with (~P) (~P ∨ ~P) (Q ∨ R).
  intros n4_37b.
  MP n4_37b n4_25a.
  replace (¬ P ∨ ¬ P ∨ Q) with ((¬ P ∨ ¬ P) ∨ Q) in n4_2a.
  replace (((¬ P ∨ ¬ P) ∨ Q) ∨ R) with ((¬ P ∨ ¬ P) ∨ Q ∨ R) in n4_2a.
  replace ((¬ P ∨ ¬ P) ∨ Q ∨ R) with ((¬ P) ∨ (Q ∨ R)) in n4_2a.
  replace (¬ P ∨ Q ∨ R) with (P → (Q ∨ R)) in n4_2a.
  apply n4_2a.
  apply Impl1_01.
  apply EqBi.
  apply n4_37b.
  apply n2_33.
  replace ((¬ P ∨ ¬ P) ∨ Q) with (¬ P ∨ ¬ P ∨ Q).
  reflexivity.
  apply n2_33.
  replace ((¬ P ∨ ¬ P ∨ Q) ∨ R) with (¬ P ∨ (¬ P ∨ Q) ∨ R).
  reflexivity.
  apply EqBi.
  apply n4_33b.
  apply EqBi.
  apply n4_37a.
  replace ((Q ∨ ¬ P) ∨ R) with (Q ∨ ¬ P ∨ R).
  reflexivity.
  apply n2_33.
  apply EqBi.
  apply n4_33a.
  replace (¬ P ∨ Q) with (P→Q).
  replace (¬ P ∨ R) with (P→R).
  reflexivity.
  apply Impl1_01.
  apply Impl1_01.
  Qed.

Theorem n4_79 : ∀ P Q R : Prop,
  ((Q → P) ∨ (R → P)) ↔ ((Q ∧ R) → P).
  Proof. intros P Q R.
    specialize Trans4_1 with Q P.
    intros Trans4_1a.
    specialize Trans4_1 with R P.
    intros Trans4_1b.
    Conj Trans4_1a Trans4_1b.
    split.
    apply Trans4_1a.
    apply Trans4_1b.
    specialize n4_39 with (Q→P) (R→P) (~P→~Q) (~P→~R).
    intros n4_39a.
    MP n4_39a H.
    specialize n4_78 with (~P) (~Q) (~R).
    intros n4_78a.
    replace ((¬ P → ¬ Q) ∨ (¬ P → ¬ R)) with (¬ P → ¬ Q ∨ ¬ R) in n4_39a.
    specialize Trans2_15 with P (~Q ∨ ~R).
    intros Trans2_15a.
    replace (¬ P → ¬ Q ∨ ¬ R) with (¬ (¬ Q ∨ ¬ R) → P) in n4_39a.
    replace (~(~Q ∨ ~R)) with (Q ∧ R) in n4_39a.
    apply n4_39a.
    apply Prod3_01.
    replace (¬ (¬ Q ∨ ¬ R) → P) with (¬ P → ¬ Q ∨ ¬ R).
    reflexivity.
    apply EqBi.
    split.
    apply Trans2_15a.
    apply Trans2_15.
    replace (¬ P → ¬ Q ∨ ¬ R) with ((¬ P → ¬ Q) ∨ (¬ P → ¬ R)).
    reflexivity.
    apply EqBi.
    apply n4_78a.
  Qed.

Theorem n4_8 : ∀ P : Prop,
  (P → ~P) ↔ ~P.
  Proof. intros P.
    specialize Abs2_01 with P.
    intros Abs2_01a.
    specialize  n2_02 with P (~P).
    intros n2_02a.
    Conj Abs2_01a n2_02a.
    split.
    apply Abs2_01a.
    apply n2_02a.
    Equiv H.
    apply H.
    apply Equiv4_01.
  Qed.

Theorem n4_81 : ∀ P : Prop,
  (~P → P) ↔ P.
  Proof. intros P.
    specialize n2_18 with P.
    intros n2_18a.
    specialize  n2_02 with (~P) P.
    intros n2_02a.
    Conj n2_18a n2_02a.
    split.
    apply n2_18a.
    apply n2_02a.
    Equiv H.
    apply H.
    apply Equiv4_01.
  Qed.

Theorem n4_82 : ∀ P Q : Prop,
  ((P → Q) ∧ (P → ~Q)) ↔ ~P.
  Proof. intros P Q. 
    specialize n2_65 with P Q.
    intros n2_65a.
    specialize Imp3_31 with (P→Q) (P→~Q) (~P).
    intros Imp3_31a.
    MP Imp3_31a n2_65a.
    specialize n2_21 with P Q.
    intros n2_21a.
    specialize n2_21 with P (~Q).
    intros n2_21b.
    Conj n2_21a n2_21b.
    split.
    apply n2_21a.
    apply n2_21b.
    specialize Comp3_43 with (~P) (P→Q) (P→~Q).
    intros Comp3_43a.
    MP Comp3_43a H.
    clear n2_65a. clear n2_21a. clear n2_21b.
    clear H.
    Conj Imp3_31a Comp3_43a.
    split.
    apply Imp3_31a.
    apply Comp3_43a.
    Equiv H.
    apply H.
    apply Equiv4_01.
  Qed.

Theorem n4_83 : ∀ P Q : Prop,
  ((P → Q) ∧ (~P → Q)) ↔ Q.
  Proof. intros P Q.
  specialize n2_61 with P Q.
  intros n2_61a.
  specialize Imp3_31 with (P→Q) (~P→Q) (Q).
  intros Imp3_31a.
  MP Imp3_31a n2_61a.
  specialize n2_02 with P Q.
  intros n2_02a.
  specialize n2_02 with (~P) Q.
  intros n2_02b.
  Conj n2_02a n2_02b.
  split.
  apply n2_02a.
  apply n2_02b.
  specialize Comp3_43 with Q (P→Q) (~P→Q).
  intros Comp3_43a.
  MP Comp3_43a H.
  clear n2_61a. clear n2_02a. clear n2_02b.
  clear H.
  Conj Imp3_31a Comp3_43a.
  split.
  apply Imp3_31a.
  apply Comp3_43a.
  Equiv H.
  apply H.
  apply Equiv4_01.
  Qed.

Theorem n4_84 : ∀ P Q R : Prop,
  (P ↔ Q) → ((P → R) ↔ (Q → R)).
  Proof. intros P Q R.
    specialize Syll2_06 with P Q R.
    intros Syll2_06a.
    specialize Syll2_06 with Q P R.
    intros Syll2_06b.
    Conj Syll2_06a Syll2_06b.
    split.
    apply Syll2_06a.
    apply Syll2_06b.
    specialize n3_47 with (P→Q) (Q→P) ((Q→R)→P→R) ((P→R)→Q→R).
    intros n3_47a.
    MP n3_47a H.
    replace ((P→Q) ∧ (Q → P)) with (P↔Q) in n3_47a.
    replace (((Q → R) → P → R) ∧ ((P → R) → Q → R)) with ((Q → R) ↔ (P → R)) in n3_47a.
    replace ((Q → R) ↔ (P → R)) with ((P→ R) ↔ (Q → R)) in n3_47a.
    apply n3_47a.
    apply EqBi.
    apply n4_21.
    apply Equiv4_01.
    apply Equiv4_01.
  Qed.

Theorem n4_85 : ∀ P Q R : Prop,
  (P ↔ Q) → ((R → P) ↔ (R → Q)).
  Proof. intros P Q R.
  specialize Syll2_05 with R P Q.
  intros Syll2_05a.
  specialize Syll2_05 with R Q P.
  intros Syll2_05b.
  Conj Syll2_05a Syll2_05b.
  split.
  apply Syll2_05a.
  apply Syll2_05b.
  specialize n3_47 with (P→Q) (Q→P) ((R→P)→R→Q) ((R→Q)→R→P).
  intros n3_47a.
  MP n3_47a H.
  replace ((P→Q) ∧ (Q → P)) with (P↔Q) in n3_47a.
  replace (((R → P) → R → Q) ∧ ((R → Q) → R → P)) with ((R → P) ↔ (R → Q)) in n3_47a.
  apply n3_47a.
  apply Equiv4_01.
  apply Equiv4_01.
Qed.

Theorem n4_86 : ∀ P Q R : Prop,
  (P ↔ Q) → ((P ↔ R) ↔ (Q ↔ R)).
  Proof. intros P Q R.
  split.
  split.
  replace (P↔Q) with (Q↔P) in H.
  Conj H H0.
  split.
  apply H.
  apply H0.
  specialize n4_22 with  Q P R.
  intros n4_22a.
  MP n4_22a H1.
  replace (Q ↔ R) with ((Q→R) ∧ (R→Q)) in n4_22a.
  specialize Simp3_26 with (Q→R) (R→Q).
  intros Simp3_26a.
  MP Simp3_26a n4_22a.
  apply Simp3_26a.
  apply Equiv4_01.
  apply EqBi.
  apply n4_21.
  replace (P↔R) with (R↔P) in H0.
  Conj H0 H.
  split.
  apply H.
  apply H0.
  replace ((P ↔ Q) ∧ (R ↔ P)) with ((R ↔ P) ∧ (P ↔ Q)) in H1.
  specialize n4_22 with R P Q.
  intros n4_22a.
  MP n4_22a H1.
  replace (R ↔ Q) with ((R→Q) ∧ (Q→R)) in n4_22a.
  specialize Simp3_26 with (R→Q) (Q→R).
  intros Simp3_26a.
  MP Simp3_26a n4_22a.
  apply Simp3_26a.
  apply Equiv4_01.
  apply EqBi.
  apply n4_3.
  apply EqBi.
  apply n4_21.
  split.
  Conj H H0.
  split.
  apply H.
  apply H0.
  specialize n4_22 with P Q R.
  intros n4_22a.
  MP n4_22a H1.
  replace (P↔R) with ((P→R)∧(R→P)) in n4_22a.
  specialize Simp3_26 with (P→R) (R→P).
  intros Simp3_26a.
  MP Simp3_26a n4_22a.
  apply Simp3_26a.
  apply Equiv4_01.
  Conj H H0.
  split.
  apply H.
  apply H0.
  specialize n4_22 with P Q R.
  intros n4_22a.
  MP n4_22a H1.
  replace (P↔R) with ((P→R)∧(R→P)) in n4_22a.
  specialize Simp3_27 with (P→R) (R→P).
  intros Simp3_27a.
  MP Simp3_27a n4_22a.
  apply Simp3_27a.
  apply Equiv4_01.
  Qed.

Theorem n4_87 : ∀ P Q R : Prop,
  (((P ∧ Q) → R) ↔ (P → Q → R)) ↔ ((Q → (P → R)) ↔ (Q ∧ P → R)).
  Proof. intros P Q R.
  specialize Exp3_3 with P Q R.
  intros Exp3_3a.
  specialize Imp3_31 with P Q R.
  intros Imp3_31a.
  Conj Exp3_3a Imp3_31a.
  split.
  apply Exp3_3a.
  apply Imp3_31a.
  Equiv H.
  specialize Exp3_3 with Q P R.
  intros Exp3_3b.
  specialize Imp3_31 with Q P R.
  intros Imp3_31b.
  Conj Exp3_3b Imp3_31b.
  split.
  apply Exp3_3b.
  apply Imp3_31b.
  Equiv H0.
  specialize Comm2_04 with P Q R.
  intros Comm2_04a.
  specialize Comm2_04 with Q P R.
  intros Comm2_04b.
  Conj Comm2_04a Comm2_04b.
  split.
  apply Comm2_04a.
  apply Comm2_04b.
  Equiv H1.
  clear Exp3_3a. clear Imp3_31a. clear Exp3_3b. clear Imp3_31b. clear Comm2_04a. clear Comm2_04b.
  replace (P ∧ Q → R) with (P → Q → R).
  replace (Q ∧ P → R) with (Q → P → R).
  replace (Q → P → R) with (P → Q → R).
  specialize n4_2 with ((P → Q → R) ↔ (P → Q → R)).
  intros n4_2a.
  apply n4_2a.
  apply EqBi.
  apply H1.
  replace (Q → P → R) with (Q ∧ P → R).
  reflexivity.
  apply EqBi.
  apply H0.
  replace (P → Q → R) with (P ∧ Q → R).
  reflexivity.
  apply EqBi.
  apply H.
  apply Equiv4_01.
  apply Equiv4_01.
  apply Equiv4_01.
  Qed.

End No4.