src/HOL/Extraction/Euclid.thy
 author wenzelm Tue, 07 Jul 2009 20:16:06 +0200 changeset 31953 eeb8a300f362 parent 30047 46c88406e6c0 child 32479 521cc9bf2958 permissions -rw-r--r--
fixed proof (cf. 40501bb2d57c);
```
(*  Title:      HOL/Extraction/Euclid.thy
ID:         \$Id\$
Author:     Markus Wenzel, TU Muenchen
Stefan Berghofer, TU Muenchen
*)

theory Euclid
imports "~~/src/HOL/NumberTheory/Factorization" Util Efficient_Nat
begin

text {*
A constructive version of the proof of Euclid's theorem by
Markus Wenzel and Freek Wiedijk \cite{Wenzel-Wiedijk-JAR2002}.
*}

lemma prime_eq: "prime p = (1 < p \<and> (\<forall>m. m dvd p \<longrightarrow> 1 < m \<longrightarrow> m = p))"
apply (rule iffI)
apply blast
apply (erule conjE)
apply (rule conjI)
apply assumption
apply (rule allI impI)+
apply (erule allE)
apply (erule impE)
apply assumption
apply (case_tac "m=0")
apply simp
apply (case_tac "m=Suc 0")
apply simp
apply simp
done

lemma prime_eq': "prime p = (1 < p \<and> (\<forall>m k. p = m * k \<longrightarrow> 1 < m \<longrightarrow> m = p))"
by (simp add: prime_eq dvd_def all_simps [symmetric] del: all_simps)

lemma factor_greater_one1: "n = m * k \<Longrightarrow> m < n \<Longrightarrow> k < n \<Longrightarrow> Suc 0 < m"
by (induct m) auto

lemma factor_greater_one2: "n = m * k \<Longrightarrow> m < n \<Longrightarrow> k < n \<Longrightarrow> Suc 0 < k"
by (induct k) auto

lemma not_prime_ex_mk:
assumes n: "Suc 0 < n"
shows "(\<exists>m k. Suc 0 < m \<and> Suc 0 < k \<and> m < n \<and> k < n \<and> n = m * k) \<or> prime n"
proof -
{
fix k
from nat_eq_dec
have "(\<exists>m<n. n = m * k) \<or> \<not> (\<exists>m<n. n = m * k)"
by (rule search)
}
hence "(\<exists>k<n. \<exists>m<n. n = m * k) \<or> \<not> (\<exists>k<n. \<exists>m<n. n = m * k)"
by (rule search)
thus ?thesis
proof
assume "\<exists>k<n. \<exists>m<n. n = m * k"
then obtain k m where k: "k<n" and m: "m<n" and nmk: "n = m * k"
by iprover
from nmk m k have "Suc 0 < m" by (rule factor_greater_one1)
moreover from nmk m k have "Suc 0 < k" by (rule factor_greater_one2)
ultimately show ?thesis using k m nmk by iprover
next
assume "\<not> (\<exists>k<n. \<exists>m<n. n = m * k)"
hence A: "\<forall>k<n. \<forall>m<n. n \<noteq> m * k" by iprover
have "\<forall>m k. n = m * k \<longrightarrow> Suc 0 < m \<longrightarrow> m = n"
proof (intro allI impI)
fix m k
assume nmk: "n = m * k"
assume m: "Suc 0 < m"
from n m nmk have k: "0 < k"
by (cases k) auto
moreover from n have n: "0 < n" by simp
moreover note m
moreover from nmk have "m * k = n" by simp
ultimately have kn: "k < n" by (rule prod_mn_less_k)
show "m = n"
proof (cases "k = Suc 0")
case True
with nmk show ?thesis by (simp only: mult_Suc_right)
next
case False
from m have "0 < m" by simp
moreover note n
moreover from False n nmk k have "Suc 0 < k" by auto
moreover from nmk have "k * m = n" by (simp only: mult_ac)
ultimately have mn: "m < n" by (rule prod_mn_less_k)
with kn A nmk show ?thesis by iprover
qed
qed
with n have "prime n"
by (simp only: prime_eq' One_nat_def simp_thms)
thus ?thesis ..
qed
qed

lemma factor_exists: "Suc 0 < n \<Longrightarrow> (\<exists>l. primel l \<and> prod l = n)"
proof (induct n rule: nat_wf_ind)
case (1 n)
from `Suc 0 < n`
have "(\<exists>m k. Suc 0 < m \<and> Suc 0 < k \<and> m < n \<and> k < n \<and> n = m * k) \<or> prime n"
by (rule not_prime_ex_mk)
then show ?case
proof
assume "\<exists>m k. Suc 0 < m \<and> Suc 0 < k \<and> m < n \<and> k < n \<and> n = m * k"
then obtain m k where m: "Suc 0 < m" and k: "Suc 0 < k" and mn: "m < n"
and kn: "k < n" and nmk: "n = m * k" by iprover
from mn and m have "\<exists>l. primel l \<and> prod l = m" by (rule 1)
then obtain l1 where primel_l1: "primel l1" and prod_l1_m: "prod l1 = m"
by iprover
from kn and k have "\<exists>l. primel l \<and> prod l = k" by (rule 1)
then obtain l2 where primel_l2: "primel l2" and prod_l2_k: "prod l2 = k"
by iprover
from primel_l1 primel_l2
have "\<exists>l. primel l \<and> prod l = prod l1 * prod l2"
by (rule split_primel)
with prod_l1_m prod_l2_k nmk show ?thesis by simp
next
assume "prime n"
hence "primel [n] \<and> prod [n] = n" by (rule prime_primel)
thus ?thesis ..
qed
qed

lemma dvd_prod [iff]: "n dvd prod (n # ns)"
by simp

primrec fact :: "nat \<Rightarrow> nat"    ("(_!)"  999)
where
"0! = 1"
| "(Suc n)! = n! * Suc n"

lemma fact_greater_0 [iff]: "0 < n!"
by (induct n) simp_all

lemma dvd_factorial: "0 < m \<Longrightarrow> m \<le> n \<Longrightarrow> m dvd n!"
proof (induct n)
case 0
then show ?case by simp
next
case (Suc n)
from `m \<le> Suc n` show ?case
proof (rule le_SucE)
assume "m \<le> n"
with `0 < m` have "m dvd n!" by (rule Suc)
then have "m dvd (n! * Suc n)" by (rule dvd_mult2)
then show ?thesis by simp
next
assume "m = Suc n"
then have "m dvd (n! * Suc n)"
by (auto intro: dvdI simp: mult_ac)
then show ?thesis by simp
qed
qed

lemma prime_factor_exists:
assumes N: "(1::nat) < n"
shows "\<exists>p. prime p \<and> p dvd n"
proof -
from N obtain l where primel_l: "primel l"
and prod_l: "n = prod l" using factor_exists
by simp iprover
from prems have "l \<noteq> []"
then obtain x xs where l: "l = x # xs"
by (cases l) simp
from primel_l l have "prime x" by (simp add: primel_hd_tl)
moreover from primel_l l prod_l
have "x dvd n" by (simp only: dvd_prod)
ultimately show ?thesis by iprover
qed

text {*
Euclid's theorem: there are infinitely many primes.
*}

lemma Euclid: "\<exists>p. prime p \<and> n < p"
proof -
let ?k = "n! + 1"
have "1 < n! + 1" by simp
then obtain p where prime: "prime p" and dvd: "p dvd ?k" using prime_factor_exists by iprover
have "n < p"
proof -
have "\<not> p \<le> n"
proof
assume pn: "p \<le> n"
from `prime p` have "0 < p" by (rule prime_g_zero)
then have "p dvd n!" using pn by (rule dvd_factorial)
with dvd have "p dvd ?k - n!" by (rule dvd_diff_nat)
then have "p dvd 1" by simp
with prime show False using prime_nd_one by auto
qed
then show ?thesis by simp
qed
with prime show ?thesis by iprover
qed

extract Euclid

text {*
The program extracted from the proof of Euclid's theorem looks as follows.
@{thm [display] Euclid_def}
The program corresponding to the proof of the factorization theorem is
@{thm [display] factor_exists_def}
*}

instantiation nat :: default
begin

definition "default = (0::nat)"

instance ..

end

instantiation list :: (type) default
begin

definition "default = []"

instance ..

end

consts_code
default ("(error \"default\")")

lemma "factor_exists 1007 = [53, 19]" by evaluation
lemma "factor_exists 1007 = [53, 19]" by eval

lemma "factor_exists 567 = [7, 3, 3, 3, 3]" by evaluation
lemma "factor_exists 567 = [7, 3, 3, 3, 3]" by eval

lemma "factor_exists 345 = [23, 5, 3]" by evaluation
lemma "factor_exists 345 = [23, 5, 3]" by eval

lemma "factor_exists 999 = [37, 3, 3, 3]" by evaluation
lemma "factor_exists 999 = [37, 3, 3, 3]" by eval

lemma "factor_exists 876 = [73, 3, 2, 2]" by evaluation
lemma "factor_exists 876 = [73, 3, 2, 2]" by eval

primrec iterate :: "nat \<Rightarrow> ('a \<Rightarrow> 'a) \<Rightarrow> 'a \<Rightarrow> 'a list" where
"iterate 0 f x = []"
| "iterate (Suc n) f x = (let y = f x in y # iterate n f y)"

lemma "iterate 4 Euclid 0 = [2, 3, 7, 71]" by evaluation
lemma "iterate 4 Euclid 0 = [2, 3, 7, 71]" by eval

end
```