PL fully checked in Coq

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+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.
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