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authorDavid Aspinall2010-08-03 12:47:35 +0000
committerDavid Aspinall2010-08-03 12:47:35 +0000
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treebe54a20538c175202bbdddf804da01daab705307 /isar/Root2_Tactic.thy
parent123f667b9b8e2c37f13f3fc0f5176863f15dd5c5 (diff)
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-(* Example proof by Larry Paulson; see http://www.cs.kun.nl/~freek/comparison/
- Taken from Isabelle2005 distribution. *)
-
-
-(* Title: HOL/Hyperreal/ex/Sqrt_Script.thy
- ID: $Id$
- Author: Lawrence C Paulson, Cambridge University Computer Laboratory
- Copyright 2001 University of Cambridge
-*)
-
-header {* Square roots of primes are irrational (script version) *}
-
-theory Root2_Tactic
-imports Primes Complex_Main
-begin
-
-text {*
- \medskip Contrast this linear Isabelle/Isar script with Markus
- Wenzel's more mathematical version.
-*}
-
-subsection {* Preliminaries *}
-
-lemma prime_nonzero: "prime p \<Longrightarrow> p \<noteq> 0"
- by (force simp add: prime_def)
-
-lemma prime_dvd_other_side:
- "n * n = p * (k * k) \<Longrightarrow> prime p \<Longrightarrow> p dvd n"
- apply (subgoal_tac "p dvd n * n", blast dest: prime_dvd_mult)
- apply (rule_tac j = "k * k" in dvd_mult_left, simp)
- done
-
-lemma reduction: "prime p \<Longrightarrow>
- 0 < k \<Longrightarrow> k * k = p * (j * j) \<Longrightarrow> k < p * j \<and> 0 < j"
- apply (rule ccontr)
- apply (simp add: linorder_not_less)
- apply (erule disjE)
- apply (frule mult_le_mono, assumption)
- apply auto
- apply (force simp add: prime_def)
- done
-
-lemma rearrange: "(j::nat) * (p * j) = k * k \<Longrightarrow> k * k = p * (j * j)"
- by (simp add: mult_ac)
-
-lemma prime_not_square:
- "prime p \<Longrightarrow> (\<And>k. 0 < k \<Longrightarrow> m * m \<noteq> p * (k * k))"
- apply (induct m rule: nat_less_induct)
- apply clarify
- apply (frule prime_dvd_other_side, assumption)
- apply (erule dvdE)
- apply (simp add: nat_mult_eq_cancel_disj prime_nonzero)
- apply (blast dest: rearrange reduction)
- done
-
-
-subsection {* The set of rational numbers *}
-
-constdefs
- rationals :: "real set" ("\<rat>")
- "\<rat> \<equiv> {x. \<exists>m n. n \<noteq> 0 \<and> \<bar>x\<bar> = real (m::nat) / real (n::nat)}"
-
-
-subsection {* Main theorem *}
-
-text {*
- The square root of any prime number (including @{text 2}) is
- irrational.
-*}
-
-theorem prime_sqrt_irrational:
- "prime p \<Longrightarrow> x * x = real p \<Longrightarrow> 0 \<le> x \<Longrightarrow> x \<notin> \<rat>"
- apply (simp add: rationals_def real_abs_def)
- apply clarify
- apply (erule_tac P = "real m / real n * ?x = ?y" in rev_mp)
- apply (simp del: real_of_nat_mult
- add: divide_eq_eq prime_not_square real_of_nat_mult [symmetric])
- done
-
-lemmas two_sqrt_irrational =
- prime_sqrt_irrational [OF two_is_prime]
-
-end