src/HOL/Number_Theory/Primes.thy
 author nipkow Wed, 05 Nov 2014 19:43:17 +0100 changeset 58898 1ebf0a1f12a4 parent 58889 5b7a9633cfa8 child 58954 18750e86d5b8 permissions -rw-r--r--
reduced execution time
```
(*  Authors:    Christophe Tabacznyj, Lawrence C. Paulson, Amine Chaieb,
Thomas M. Rasmussen, Jeremy Avigad, Tobias Nipkow

This file deals with properties of primes. Definitions and lemmas are
proved uniformly for the natural numbers and integers.

This file combines and revises a number of prior developments.

The original theories "GCD" and "Primes" were by Christophe Tabacznyj
and Lawrence C. Paulson, based on @{cite davenport92}. They introduced
gcd, lcm, and prime for the natural numbers.

The original theory "IntPrimes" was by Thomas M. Rasmussen, and
extended gcd, lcm, primes to the integers. Amine Chaieb provided
another extension of the notions to the integers, and added a number
of results to "Primes" and "GCD". IntPrimes also defined and developed
the congruence relations on the integers. The notion was extended to
the natural numbers by Chaieb.

natural numbers and the integers, and added a number of new theorems.

Tobias Nipkow cleaned up a lot.
*)

section {* Primes *}

theory Primes
imports "~~/src/HOL/GCD"
begin

declare [[coercion int]]
declare [[coercion_enabled]]

definition prime :: "nat \<Rightarrow> bool"
where "prime p = (1 < p \<and> (\<forall>m. m dvd p --> m = 1 \<or> m = p))"

lemmas prime_nat_def = prime_def

subsection {* Primes *}

lemma prime_odd_nat: "prime p \<Longrightarrow> p > 2 \<Longrightarrow> odd p"
apply (auto simp add: prime_nat_def even_iff_mod_2_eq_zero dvd_eq_mod_eq_0)
apply (metis dvd_eq_mod_eq_0 even_Suc even_iff_mod_2_eq_zero mod_by_1 nat_dvd_not_less not_mod_2_eq_0_eq_1 zero_less_numeral)
done

(* FIXME Is there a better way to handle these, rather than making them elim rules? *)

lemma prime_gt_0_nat [elim]: "prime p \<Longrightarrow> p > 0"
unfolding prime_nat_def by auto

lemma prime_ge_1_nat [elim]: "prime p \<Longrightarrow> p >= 1"
unfolding prime_nat_def by auto

lemma prime_gt_1_nat [elim]: "prime p \<Longrightarrow> p > 1"
unfolding prime_nat_def by auto

lemma prime_ge_Suc_0_nat [elim]: "prime p \<Longrightarrow> p >= Suc 0"
unfolding prime_nat_def by auto

lemma prime_gt_Suc_0_nat [elim]: "prime p \<Longrightarrow> p > Suc 0"
unfolding prime_nat_def by auto

lemma prime_ge_2_nat [elim]: "prime p \<Longrightarrow> p >= 2"
unfolding prime_nat_def by auto

lemma prime_imp_coprime_nat: "prime p \<Longrightarrow> \<not> p dvd n \<Longrightarrow> coprime p n"
apply (unfold prime_nat_def)
apply (metis gcd_dvd1_nat gcd_dvd2_nat)
done

lemma prime_int_altdef:
"prime p = (1 < p \<and> (\<forall>m::int. m \<ge> 0 \<longrightarrow> m dvd p \<longrightarrow>
m = 1 \<or> m = p))"
apply (metis One_nat_def int_1 nat_0_le nat_dvd_iff)
apply (metis zdvd_int One_nat_def le0 of_nat_0 of_nat_1 of_nat_eq_iff of_nat_le_iff)
done

lemma prime_imp_coprime_int:
fixes n::int shows "prime p \<Longrightarrow> \<not> p dvd n \<Longrightarrow> coprime p n"
apply (unfold prime_int_altdef)
apply (metis gcd_dvd1_int gcd_dvd2_int gcd_ge_0_int)
done

lemma prime_dvd_mult_nat: "prime p \<Longrightarrow> p dvd m * n \<Longrightarrow> p dvd m \<or> p dvd n"
by (blast intro: coprime_dvd_mult_nat prime_imp_coprime_nat)

lemma prime_dvd_mult_int:
fixes n::int shows "prime p \<Longrightarrow> p dvd m * n \<Longrightarrow> p dvd m \<or> p dvd n"
by (blast intro: coprime_dvd_mult_int prime_imp_coprime_int)

lemma prime_dvd_mult_eq_nat [simp]: "prime p \<Longrightarrow>
p dvd m * n = (p dvd m \<or> p dvd n)"
by (rule iffI, rule prime_dvd_mult_nat, auto)

lemma prime_dvd_mult_eq_int [simp]:
fixes n::int
shows "prime p \<Longrightarrow> p dvd m * n = (p dvd m \<or> p dvd n)"
by (rule iffI, rule prime_dvd_mult_int, auto)

lemma not_prime_eq_prod_nat: "(n::nat) > 1 \<Longrightarrow> ~ prime n \<Longrightarrow>
EX m k. n = m * k & 1 < m & m < n & 1 < k & k < n"
unfolding prime_nat_def dvd_def apply auto
by (metis mult.commute linorder_neq_iff linorder_not_le mult_1
n_less_n_mult_m one_le_mult_iff less_imp_le_nat)

lemma prime_dvd_power_nat: "prime p \<Longrightarrow> p dvd x^n \<Longrightarrow> p dvd x"
by (induct n) auto

lemma prime_dvd_power_int:
fixes x::int shows "prime p \<Longrightarrow> p dvd x^n \<Longrightarrow> p dvd x"
by (induct n) auto

lemma prime_dvd_power_nat_iff: "prime p \<Longrightarrow> n > 0 \<Longrightarrow>
p dvd x^n \<longleftrightarrow> p dvd x"
by (cases n) (auto elim: prime_dvd_power_nat)

lemma prime_dvd_power_int_iff:
fixes x::int
shows "prime p \<Longrightarrow> n > 0 \<Longrightarrow> p dvd x^n \<longleftrightarrow> p dvd x"
by (cases n) (auto elim: prime_dvd_power_int)

subsubsection {* Make prime naively executable *}

lemma zero_not_prime_nat [simp]: "~prime (0::nat)"

lemma one_not_prime_nat [simp]: "~prime (1::nat)"

lemma Suc_0_not_prime_nat [simp]: "~prime (Suc 0)"

lemma prime_nat_code [code]:
"prime p \<longleftrightarrow> p > 1 \<and> (\<forall>n \<in> {1<..<p}. ~ n dvd p)"
apply (metis One_nat_def less_not_refl prime_nat_def dvd_triv_right not_prime_eq_prod_nat)
done

lemma prime_nat_simp:
"prime p \<longleftrightarrow> p > 1 \<and> (\<forall>n \<in> set [2..<p]. \<not> n dvd p)"

lemmas prime_nat_simp_numeral [simp] = prime_nat_simp [of "numeral m"] for m

lemma two_is_prime_nat [simp]: "prime (2::nat)"
by simp

text{* A bit of regression testing: *}

lemma "prime(7::nat)" by simp
lemma "prime(997::nat)" by eval

lemma prime_imp_power_coprime_nat: "prime p \<Longrightarrow> ~ p dvd a \<Longrightarrow> coprime a (p^m)"
by (metis coprime_exp_nat gcd_nat.commute prime_imp_coprime_nat)

lemma prime_imp_power_coprime_int:
fixes a::int shows "prime p \<Longrightarrow> ~ p dvd a \<Longrightarrow> coprime a (p^m)"
by (metis coprime_exp_int gcd_int.commute prime_imp_coprime_int)

lemma primes_coprime_nat: "prime p \<Longrightarrow> prime q \<Longrightarrow> p \<noteq> q \<Longrightarrow> coprime p q"
by (metis gcd_nat.absorb1 gcd_nat.absorb2 prime_imp_coprime_nat)

lemma primes_imp_powers_coprime_nat:
"prime p \<Longrightarrow> prime q \<Longrightarrow> p ~= q \<Longrightarrow> coprime (p^m) (q^n)"
by (rule coprime_exp2_nat, rule primes_coprime_nat)

lemma prime_factor_nat: "n \<noteq> (1::nat) \<Longrightarrow> \<exists> p. prime p \<and> p dvd n"
apply (induct n rule: nat_less_induct)
apply (case_tac "n = 0")
using two_is_prime_nat
apply blast
apply (metis One_nat_def dvd.order_trans dvd_refl less_Suc0 linorder_neqE_nat
nat_dvd_not_less neq0_conv prime_nat_def)
done

text {* One property of coprimality is easier to prove via prime factors. *}

lemma prime_divprod_pow_nat:
assumes p: "prime p" and ab: "coprime a b" and pab: "p^n dvd a * b"
shows "p^n dvd a \<or> p^n dvd b"
proof-
{ assume "n = 0 \<or> a = 1 \<or> b = 1" with pab have ?thesis
apply (cases "n=0", simp_all)
apply (cases "a=1", simp_all)
done }
moreover
{ assume n: "n \<noteq> 0" and a: "a\<noteq>1" and b: "b\<noteq>1"
then obtain m where m: "n = Suc m" by (cases n) auto
from n have "p dvd p^n" apply (intro dvd_power) apply auto done
also note pab
finally have pab': "p dvd a * b".
from prime_dvd_mult_nat[OF p pab']
have "p dvd a \<or> p dvd b" .
moreover
{ assume pa: "p dvd a"
from coprime_common_divisor_nat [OF ab, OF pa] p have "\<not> p dvd b" by auto
with p have "coprime b p"
by (subst gcd_commute_nat, intro prime_imp_coprime_nat)
then have pnb: "coprime (p^n) b"
by (subst gcd_commute_nat, rule coprime_exp_nat)
from coprime_dvd_mult_nat[OF pnb pab] have ?thesis by blast }
moreover
{ assume pb: "p dvd b"
have pnba: "p^n dvd b*a" using pab by (simp add: mult.commute)
from coprime_common_divisor_nat [OF ab, of p] pb p have "\<not> p dvd a"
by auto
with p have "coprime a p"
by (subst gcd_commute_nat, intro prime_imp_coprime_nat)
then have pna: "coprime (p^n) a"
by (subst gcd_commute_nat, rule coprime_exp_nat)
from coprime_dvd_mult_nat[OF pna pnba] have ?thesis by blast }
ultimately have ?thesis by blast }
ultimately show ?thesis by blast
qed

subsection {* Infinitely many primes *}

lemma next_prime_bound: "\<exists>p. prime p \<and> n < p \<and> p <= fact n + 1"
proof-
have f1: "fact n + 1 \<noteq> 1" using fact_ge_one_nat [of n] by arith
from prime_factor_nat [OF f1]
obtain p where "prime p" and "p dvd fact n + 1" by auto
then have "p \<le> fact n + 1" apply (intro dvd_imp_le) apply auto done
{ assume "p \<le> n"
from `prime p` have "p \<ge> 1"
by (cases p, simp_all)
with `p <= n` have "p dvd fact n"
by (intro dvd_fact_nat)
with `p dvd fact n + 1` have "p dvd fact n + 1 - fact n"
by (rule dvd_diff_nat)
then have "p dvd 1" by simp
then have "p <= 1" by auto
moreover from `prime p` have "p > 1" by auto
ultimately have False by auto}
then have "n < p" by presburger
with `prime p` and `p <= fact n + 1` show ?thesis by auto
qed

lemma bigger_prime: "\<exists>p. prime p \<and> p > (n::nat)"
using next_prime_bound by auto

lemma primes_infinite: "\<not> (finite {(p::nat). prime p})"
proof
assume "finite {(p::nat). prime p}"
with Max_ge have "(EX b. (ALL x : {(p::nat). prime p}. x <= b))"
by auto
then obtain b where "ALL (x::nat). prime x \<longrightarrow> x <= b"
by auto
with bigger_prime [of b] show False
by auto
qed

subsection{*Powers of Primes*}

text{*Versions for type nat only*}

lemma prime_product:
fixes p::nat
assumes "prime (p * q)"
shows "p = 1 \<or> q = 1"
proof -
from assms have
"1 < p * q" and P: "\<And>m. m dvd p * q \<Longrightarrow> m = 1 \<or> m = p * q"
unfolding prime_nat_def by auto
from `1 < p * q` have "p \<noteq> 0" by (cases p) auto
then have Q: "p = p * q \<longleftrightarrow> q = 1" by auto
have "p dvd p * q" by simp
then have "p = 1 \<or> p = p * q" by (rule P)
then show ?thesis by (simp add: Q)
qed

lemma prime_exp:
fixes p::nat
shows "prime (p^n) \<longleftrightarrow> prime p \<and> n = 1"
proof(induct n)
case 0 thus ?case by simp
next
case (Suc n)
{assume "p = 0" hence ?case by simp}
moreover
{assume "p=1" hence ?case by simp}
moreover
{assume p: "p \<noteq> 0" "p\<noteq>1"
{assume pp: "prime (p^Suc n)"
hence "p = 1 \<or> p^n = 1" using prime_product[of p "p^n"] by simp
with p have n: "n = 0"
by (metis One_nat_def nat_power_eq_Suc_0_iff)
with pp have "prime p \<and> Suc n = 1" by simp}
moreover
{assume n: "prime p \<and> Suc n = 1" hence "prime (p^Suc n)" by simp}
ultimately have ?case by blast}
ultimately show ?case by blast
qed

lemma prime_power_mult:
fixes p::nat
assumes p: "prime p" and xy: "x * y = p ^ k"
shows "\<exists>i j. x = p ^i \<and> y = p^ j"
using xy
proof(induct k arbitrary: x y)
case 0 thus ?case apply simp by (rule exI[where x="0"], simp)
next
case (Suc k x y)
from Suc.prems have pxy: "p dvd x*y" by auto
from Primes.prime_dvd_mult_nat [OF p pxy] have pxyc: "p dvd x \<or> p dvd y" .
from p have p0: "p \<noteq> 0" by - (rule ccontr, simp)
{assume px: "p dvd x"
then obtain d where d: "x = p*d" unfolding dvd_def by blast
from Suc.prems d  have "p*d*y = p^Suc k" by simp
hence th: "d*y = p^k" using p0 by simp
from Suc.hyps[OF th] obtain i j where ij: "d = p^i" "y = p^j" by blast
with d have "x = p^Suc i" by simp
with ij(2) have ?case by blast}
moreover
{assume px: "p dvd y"
then obtain d where d: "y = p*d" unfolding dvd_def by blast
from Suc.prems d  have "p*d*x = p^Suc k" by (simp add: mult.commute)
hence th: "d*x = p^k" using p0 by simp
from Suc.hyps[OF th] obtain i j where ij: "d = p^i" "x = p^j" by blast
with d have "y = p^Suc i" by simp
with ij(2) have ?case by blast}
ultimately show ?case  using pxyc by blast
qed

lemma prime_power_exp:
fixes p::nat
assumes p: "prime p" and n: "n \<noteq> 0"
and xn: "x^n = p^k" shows "\<exists>i. x = p^i"
using n xn
proof(induct n arbitrary: k)
case 0 thus ?case by simp
next
case (Suc n k) hence th: "x*x^n = p^k" by simp
{assume "n = 0" with Suc have ?case by simp (rule exI[where x="k"], simp)}
moreover
{assume n: "n \<noteq> 0"
from prime_power_mult[OF p th]
obtain i j where ij: "x = p^i" "x^n = p^j"by blast
from Suc.hyps[OF n ij(2)] have ?case .}
ultimately show ?case by blast
qed

lemma divides_primepow:
fixes p::nat
assumes p: "prime p"
shows "d dvd p^k \<longleftrightarrow> (\<exists> i. i \<le> k \<and> d = p ^i)"
proof
assume H: "d dvd p^k" then obtain e where e: "d*e = p^k"
unfolding dvd_def  apply (auto simp add: mult.commute) by blast
from prime_power_mult[OF p e] obtain i j where ij: "d = p^i" "e=p^j" by blast
from e ij have "p^(i + j) = p^k" by (simp add: power_add)
hence "i + j = k" using p prime_gt_1_nat power_inject_exp[of p "i+j" k] by simp
hence "i \<le> k" by arith
with ij(1) show "\<exists>i\<le>k. d = p ^ i" by blast
next
{fix i assume H: "i \<le> k" "d = p^i"
then obtain j where j: "k = i + j"
hence "d dvd p^k" unfolding dvd_def by auto}
thus "\<exists>i\<le>k. d = p ^ i \<Longrightarrow> d dvd p ^ k" by blast
qed

subsection {*Chinese Remainder Theorem Variants*}

lemma bezout_gcd_nat:
fixes a::nat shows "\<exists>x y. a * x - b * y = gcd a b \<or> b * x - a * y = gcd a b"
using bezout_nat[of a b]
gcd_nat.right_neutral mult_0)

lemma gcd_bezout_sum_nat:
fixes a::nat
assumes "a * x + b * y = d"
shows "gcd a b dvd d"
proof-
let ?g = "gcd a b"
have dv: "?g dvd a*x" "?g dvd b * y"
by simp_all
show ?thesis by auto
qed

text {* A binary form of the Chinese Remainder Theorem. *}

lemma chinese_remainder:
fixes a::nat  assumes ab: "coprime a b" and a: "a \<noteq> 0" and b: "b \<noteq> 0"
shows "\<exists>x q1 q2. x = u + q1 * a \<and> x = v + q2 * b"
proof-
obtain d1 x1 y1 d2 x2 y2 where dxy1: "d1 dvd a" "d1 dvd b" "a * x1 = b * y1 + d1"
and dxy2: "d2 dvd b" "d2 dvd a" "b * x2 = a * y2 + d2" by blast
then have d12: "d1 = 1" "d2 =1"
by (metis ab coprime_nat)+
let ?x = "v * a * x1 + u * b * x2"
let ?q1 = "v * x1 + u * y2"
let ?q2 = "v * y1 + u * x2"
from dxy2(3)[simplified d12] dxy1(3)[simplified d12]
have "?x = u + ?q1 * a" "?x = v + ?q2 * b"
by algebra+
thus ?thesis by blast
qed

text {* Primality *}

lemma coprime_bezout_strong:
fixes a::nat assumes "coprime a b"  "b \<noteq> 1"
shows "\<exists>x y. a * x = b * y + 1"
by (metis assms bezout_nat gcd_nat.left_neutral)

lemma bezout_prime:
assumes p: "prime p" and pa: "\<not> p dvd a"
shows "\<exists>x y. a*x = Suc (p*y)"
proof-
have ap: "coprime a p"
by (metis gcd_nat.commute p pa prime_imp_coprime_nat)
from coprime_bezout_strong[OF ap] show ?thesis
by (metis Suc_eq_plus1 gcd_lcm_complete_lattice_nat.bot.extremum pa)
qed

end
```