wenzelm@11049: (*  Title:      HOL/NumberTheory/WilsonRuss.thy
paulson@9508:     ID:         $Id$
wenzelm@11049:     Author:     Thomas M. Rasmussen
wenzelm@11049:     Copyright   2000  University of Cambridge
paulson@9508: *)
paulson@9508: 
wenzelm@11049: header {* Wilson's Theorem according to Russinoff *}
wenzelm@11049: 
haftmann@16417: theory WilsonRuss imports EulerFermat begin
wenzelm@11049: 
wenzelm@11049: text {*
wenzelm@11049:   Wilson's Theorem following quite closely Russinoff's approach
wenzelm@11049:   using Boyer-Moore (using finite sets instead of lists, though).
wenzelm@11049: *}
wenzelm@11049: 
wenzelm@11049: subsection {* Definitions and lemmas *}
paulson@9508: 
wenzelm@19670: definition
wenzelm@21404:   inv :: "int => int => int" where
wenzelm@19670:   "inv p a = (a^(nat (p - 2))) mod p"
wenzelm@19670: 
paulson@9508: consts
wenzelm@11049:   wset :: "int * int => int set"
paulson@9508: 
wenzelm@11049: recdef wset
wenzelm@11049:   "measure ((\<lambda>(a, p). nat a) :: int * int => nat)"
wenzelm@11049:   "wset (a, p) =
paulson@11868:     (if 1 < a then
paulson@11868:       let ws = wset (a - 1, p)
wenzelm@11049:       in (if a \<in> ws then ws else insert a (insert (inv p a) ws)) else {})"
wenzelm@11049: 
wenzelm@11049: 
wenzelm@11049: text {* \medskip @{term [source] inv} *}
wenzelm@11049: 
wenzelm@13524: lemma inv_is_inv_aux: "1 < m ==> Suc (nat (m - 2)) = nat (m - 1)"
paulson@13833: by (subst int_int_eq [symmetric], auto)
wenzelm@11049: 
wenzelm@11049: lemma inv_is_inv:
nipkow@16663:     "zprime p \<Longrightarrow> 0 < a \<Longrightarrow> a < p ==> [a * inv p a = 1] (mod p)"
wenzelm@11049:   apply (unfold inv_def)
wenzelm@11049:   apply (subst zcong_zmod)
wenzelm@11049:   apply (subst zmod_zmult1_eq [symmetric])
wenzelm@11049:   apply (subst zcong_zmod [symmetric])
wenzelm@11049:   apply (subst power_Suc [symmetric])
wenzelm@13524:   apply (subst inv_is_inv_aux)
wenzelm@11049:    apply (erule_tac [2] Little_Fermat)
wenzelm@11049:    apply (erule_tac [2] zdvd_not_zless)
paulson@13833:    apply (unfold zprime_def, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_distinct:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> a \<noteq> inv p a"
wenzelm@11049:   apply safe
wenzelm@11049:   apply (cut_tac a = a and p = p in zcong_square)
paulson@13833:      apply (cut_tac [3] a = a and p = p in inv_is_inv, auto)
paulson@11868:    apply (subgoal_tac "a = 1")
wenzelm@11049:     apply (rule_tac [2] m = p in zcong_zless_imp_eq)
paulson@11868:         apply (subgoal_tac [7] "a = p - 1")
paulson@13833:          apply (rule_tac [8] m = p in zcong_zless_imp_eq, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_not_0:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> inv p a \<noteq> 0"
wenzelm@11049:   apply safe
wenzelm@11049:   apply (cut_tac a = a and p = p in inv_is_inv)
paulson@13833:      apply (unfold zcong_def, auto)
paulson@11868:   apply (subgoal_tac "\<not> p dvd 1")
wenzelm@11049:    apply (rule_tac [2] zdvd_not_zless)
paulson@11868:     apply (subgoal_tac "p dvd 1")
wenzelm@11049:      prefer 2
paulson@13833:      apply (subst zdvd_zminus_iff [symmetric], auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_not_1:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> inv p a \<noteq> 1"
wenzelm@11049:   apply safe
wenzelm@11049:   apply (cut_tac a = a and p = p in inv_is_inv)
wenzelm@11049:      prefer 4
wenzelm@11049:      apply simp
paulson@11868:      apply (subgoal_tac "a = 1")
paulson@13833:       apply (rule_tac [2] zcong_zless_imp_eq, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@19670: lemma inv_not_p_minus_1_aux:
wenzelm@19670:     "[a * (p - 1) = 1] (mod p) = [a = p - 1] (mod p)"
wenzelm@11049:   apply (unfold zcong_def)
obua@14738:   apply (simp add: OrderedGroup.diff_diff_eq diff_diff_eq2 zdiff_zmult_distrib2)
paulson@11868:   apply (rule_tac s = "p dvd -((a + 1) + (p * -a))" in trans)
paulson@14271:    apply (simp add: mult_commute)
wenzelm@11049:   apply (subst zdvd_zminus_iff)
wenzelm@11049:   apply (subst zdvd_reduce)
paulson@11868:   apply (rule_tac s = "p dvd (a + 1) + (p * -1)" in trans)
paulson@13833:    apply (subst zdvd_reduce, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_not_p_minus_1:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> inv p a \<noteq> p - 1"
wenzelm@11049:   apply safe
paulson@13833:   apply (cut_tac a = a and p = p in inv_is_inv, auto)
wenzelm@13524:   apply (simp add: inv_not_p_minus_1_aux)
paulson@11868:   apply (subgoal_tac "a = p - 1")
paulson@13833:    apply (rule_tac [2] zcong_zless_imp_eq, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_g_1:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> 1 < inv p a"
paulson@11868:   apply (case_tac "0\<le> inv p a")
paulson@11868:    apply (subgoal_tac "inv p a \<noteq> 1")
paulson@11868:     apply (subgoal_tac "inv p a \<noteq> 0")
wenzelm@11049:      apply (subst order_less_le)
wenzelm@11049:      apply (subst zle_add1_eq_le [symmetric])
wenzelm@11049:      apply (subst order_less_le)
wenzelm@11049:      apply (rule_tac [2] inv_not_0)
paulson@13833:        apply (rule_tac [5] inv_not_1, auto)
paulson@13833:   apply (unfold inv_def zprime_def, simp)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma inv_less_p_minus_1:
nipkow@16663:     "zprime p \<Longrightarrow> 1 < a \<Longrightarrow> a < p - 1 ==> inv p a < p - 1"
wenzelm@11049:   apply (case_tac "inv p a < p")
wenzelm@11049:    apply (subst order_less_le)
paulson@13833:    apply (simp add: inv_not_p_minus_1, auto)
paulson@13833:   apply (unfold inv_def zprime_def, simp)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@13524: lemma inv_inv_aux: "5 \<le> p ==>
paulson@11868:     nat (p - 2) * nat (p - 2) = Suc (nat (p - 1) * nat (p - 3))"
wenzelm@11049:   apply (subst int_int_eq [symmetric])
wenzelm@11049:   apply (simp add: zmult_int [symmetric])
wenzelm@11049:   apply (simp add: zdiff_zmult_distrib zdiff_zmult_distrib2)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma zcong_zpower_zmult:
paulson@11868:     "[x^y = 1] (mod p) \<Longrightarrow> [x^(y * z) = 1] (mod p)"
wenzelm@11049:   apply (induct z)
wenzelm@11049:    apply (auto simp add: zpower_zadd_distrib)
nipkow@15236:   apply (subgoal_tac "zcong (x^y * x^(y * z)) (1 * 1) p")
paulson@13833:    apply (rule_tac [2] zcong_zmult, simp_all)
wenzelm@11049:   done
wenzelm@11049: 
nipkow@16663: lemma inv_inv: "zprime p \<Longrightarrow>
paulson@11868:     5 \<le> p \<Longrightarrow> 0 < a \<Longrightarrow> a < p ==> inv p (inv p a) = a"
wenzelm@11049:   apply (unfold inv_def)
wenzelm@11049:   apply (subst zpower_zmod)
wenzelm@11049:   apply (subst zpower_zpower)
wenzelm@11049:   apply (rule zcong_zless_imp_eq)
wenzelm@11049:       prefer 5
wenzelm@11049:       apply (subst zcong_zmod)
wenzelm@11049:       apply (subst mod_mod_trivial)
wenzelm@11049:       apply (subst zcong_zmod [symmetric])
wenzelm@13524:       apply (subst inv_inv_aux)
wenzelm@11049:        apply (subgoal_tac [2]
paulson@11868: 	 "zcong (a * a^(nat (p - 1) * nat (p - 3))) (a * 1) p")
wenzelm@11049:         apply (rule_tac [3] zcong_zmult)
wenzelm@11049:          apply (rule_tac [4] zcong_zpower_zmult)
wenzelm@11049:          apply (erule_tac [4] Little_Fermat)
paulson@13833:          apply (rule_tac [4] zdvd_not_zless, simp_all)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: 
wenzelm@11049: text {* \medskip @{term wset} *}
wenzelm@11049: 
wenzelm@11049: declare wset.simps [simp del]
paulson@9508: 
wenzelm@11049: lemma wset_induct:
wenzelm@18369:   assumes "!!a p. P {} a p"
wenzelm@19670:     and "!!a p. 1 < (a::int) \<Longrightarrow>
wenzelm@19670:       P (wset (a - 1, p)) (a - 1) p ==> P (wset (a, p)) a p"
wenzelm@18369:   shows "P (wset (u, v)) u v"
wenzelm@18369:   apply (rule wset.induct, safe)
wenzelm@18369:    prefer 2
wenzelm@18369:    apply (case_tac "1 < a")
wenzelm@18369:     apply (rule prems)
wenzelm@18369:      apply simp_all
wenzelm@18369:    apply (simp_all add: wset.simps prems)
wenzelm@18369:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_mem_imp_or [rule_format]:
paulson@11868:   "1 < a \<Longrightarrow> b \<notin> wset (a - 1, p)
wenzelm@11049:     ==> b \<in> wset (a, p) --> b = a \<or> b = inv p a"
wenzelm@11049:   apply (subst wset.simps)
paulson@13833:   apply (unfold Let_def, simp)
wenzelm@11049:   done
wenzelm@11049: 
paulson@11868: lemma wset_mem_mem [simp]: "1 < a ==> a \<in> wset (a, p)"
wenzelm@11049:   apply (subst wset.simps)
paulson@13833:   apply (unfold Let_def, simp)
wenzelm@11049:   done
wenzelm@11049: 
paulson@11868: lemma wset_subset: "1 < a \<Longrightarrow> b \<in> wset (a - 1, p) ==> b \<in> wset (a, p)"
wenzelm@11049:   apply (subst wset.simps)
paulson@13833:   apply (unfold Let_def, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_g_1 [rule_format]:
nipkow@16663:     "zprime p --> a < p - 1 --> b \<in> wset (a, p) --> 1 < b"
paulson@13833:   apply (induct a p rule: wset_induct, auto)
wenzelm@11049:   apply (case_tac "b = a")
wenzelm@11049:    apply (case_tac [2] "b = inv p a")
wenzelm@11049:     apply (subgoal_tac [3] "b = a \<or> b = inv p a")
wenzelm@11049:      apply (rule_tac [4] wset_mem_imp_or)
wenzelm@11049:        prefer 2
wenzelm@11049:        apply simp
paulson@13833:        apply (rule inv_g_1, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_less [rule_format]:
nipkow@16663:     "zprime p --> a < p - 1 --> b \<in> wset (a, p) --> b < p - 1"
paulson@13833:   apply (induct a p rule: wset_induct, auto)
wenzelm@11049:   apply (case_tac "b = a")
wenzelm@11049:    apply (case_tac [2] "b = inv p a")
wenzelm@11049:     apply (subgoal_tac [3] "b = a \<or> b = inv p a")
wenzelm@11049:      apply (rule_tac [4] wset_mem_imp_or)
wenzelm@11049:        prefer 2
wenzelm@11049:        apply simp
paulson@13833:        apply (rule inv_less_p_minus_1, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_mem [rule_format]:
nipkow@16663:   "zprime p -->
paulson@11868:     a < p - 1 --> 1 < b --> b \<le> a --> b \<in> wset (a, p)"
paulson@13833:   apply (induct a p rule: wset.induct, auto)
nipkow@15197:   apply (rule_tac wset_subset)
nipkow@15197:   apply (simp (no_asm_simp))
nipkow@15197:   apply auto
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_mem_inv_mem [rule_format]:
nipkow@16663:   "zprime p --> 5 \<le> p --> a < p - 1 --> b \<in> wset (a, p)
wenzelm@11049:     --> inv p b \<in> wset (a, p)"
paulson@13833:   apply (induct a p rule: wset_induct, auto)
wenzelm@11049:    apply (case_tac "b = a")
wenzelm@11049:     apply (subst wset.simps)
wenzelm@11049:     apply (unfold Let_def)
paulson@13833:     apply (rule_tac [3] wset_subset, auto)
wenzelm@11049:   apply (case_tac "b = inv p a")
wenzelm@11049:    apply (simp (no_asm_simp))
wenzelm@11049:    apply (subst inv_inv)
wenzelm@11049:        apply (subgoal_tac [6] "b = a \<or> b = inv p a")
paulson@13833:         apply (rule_tac [7] wset_mem_imp_or, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_inv_mem_mem:
nipkow@16663:   "zprime p \<Longrightarrow> 5 \<le> p \<Longrightarrow> a < p - 1 \<Longrightarrow> 1 < b \<Longrightarrow> b < p - 1
wenzelm@11049:     \<Longrightarrow> inv p b \<in> wset (a, p) \<Longrightarrow> b \<in> wset (a, p)"
wenzelm@11049:   apply (rule_tac s = "inv p (inv p b)" and t = b in subst)
wenzelm@11049:    apply (rule_tac [2] wset_mem_inv_mem)
paulson@13833:       apply (rule inv_inv, simp_all)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_fin: "finite (wset (a, p))"
wenzelm@11049:   apply (induct a p rule: wset_induct)
wenzelm@11049:    prefer 2
wenzelm@11049:    apply (subst wset.simps)
paulson@13833:    apply (unfold Let_def, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: lemma wset_zcong_prod_1 [rule_format]:
nipkow@16663:   "zprime p -->
nipkow@15392:     5 \<le> p --> a < p - 1 --> [(\<Prod>x\<in>wset(a, p). x) = 1] (mod p)"
wenzelm@11049:   apply (induct a p rule: wset_induct)
wenzelm@11049:    prefer 2
wenzelm@11049:    apply (subst wset.simps)
paulson@13833:    apply (unfold Let_def, auto)
wenzelm@11049:   apply (subst setprod_insert)
wenzelm@11049:     apply (tactic {* stac (thm "setprod_insert") 3 *})
wenzelm@11049:       apply (subgoal_tac [5]
nipkow@15392: 	"zcong (a * inv p a * (\<Prod>x\<in> wset(a - 1, p). x)) (1 * 1) p")
wenzelm@11049:        prefer 5
wenzelm@11049:        apply (simp add: zmult_assoc)
wenzelm@11049:       apply (rule_tac [5] zcong_zmult)
wenzelm@11049:        apply (rule_tac [5] inv_is_inv)
wenzelm@11049:          apply (tactic "Clarify_tac 4")
paulson@11868:          apply (subgoal_tac [4] "a \<in> wset (a - 1, p)")
wenzelm@11049:           apply (rule_tac [5] wset_inv_mem_mem)
wenzelm@11049:                apply (simp_all add: wset_fin)
paulson@13833:   apply (rule inv_distinct, auto)
wenzelm@11049:   done
wenzelm@11049: 
nipkow@16663: lemma d22set_eq_wset: "zprime p ==> d22set (p - 2) = wset (p - 2, p)"
wenzelm@11049:   apply safe
wenzelm@11049:    apply (erule wset_mem)
wenzelm@11049:      apply (rule_tac [2] d22set_g_1)
wenzelm@11049:      apply (rule_tac [3] d22set_le)
wenzelm@11049:      apply (rule_tac [4] d22set_mem)
wenzelm@11049:       apply (erule_tac [4] wset_g_1)
wenzelm@11049:        prefer 6
wenzelm@11049:        apply (subst zle_add1_eq_le [symmetric])
paulson@11868:        apply (subgoal_tac "p - 2 + 1 = p - 1")
wenzelm@11049:         apply (simp (no_asm_simp))
paulson@13833:         apply (erule wset_less, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: 
wenzelm@11049: subsection {* Wilson *}
wenzelm@11049: 
nipkow@16663: lemma prime_g_5: "zprime p \<Longrightarrow> p \<noteq> 2 \<Longrightarrow> p \<noteq> 3 ==> 5 \<le> p"
wenzelm@11049:   apply (unfold zprime_def dvd_def)
paulson@13833:   apply (case_tac "p = 4", auto)
wenzelm@11049:    apply (rule notE)
wenzelm@11049:     prefer 2
wenzelm@11049:     apply assumption
wenzelm@11049:    apply (simp (no_asm))
paulson@13833:    apply (rule_tac x = 2 in exI)
paulson@13833:    apply (safe, arith)
paulson@13833:      apply (rule_tac x = 2 in exI, auto)
wenzelm@11049:   done
wenzelm@11049: 
wenzelm@11049: theorem Wilson_Russ:
nipkow@16663:     "zprime p ==> [zfact (p - 1) = -1] (mod p)"
paulson@11868:   apply (subgoal_tac "[(p - 1) * zfact (p - 2) = -1 * 1] (mod p)")
wenzelm@11049:    apply (rule_tac [2] zcong_zmult)
wenzelm@11049:     apply (simp only: zprime_def)
wenzelm@11049:     apply (subst zfact.simps)
paulson@13833:     apply (rule_tac t = "p - 1 - 1" and s = "p - 2" in subst, auto)
wenzelm@11049:    apply (simp only: zcong_def)
wenzelm@11049:    apply (simp (no_asm_simp))
wenzelm@11704:   apply (case_tac "p = 2")
wenzelm@11049:    apply (simp add: zfact.simps)
wenzelm@11704:   apply (case_tac "p = 3")
wenzelm@11049:    apply (simp add: zfact.simps)
wenzelm@11704:   apply (subgoal_tac "5 \<le> p")
wenzelm@11049:    apply (erule_tac [2] prime_g_5)
wenzelm@11049:     apply (subst d22set_prod_zfact [symmetric])
wenzelm@11049:     apply (subst d22set_eq_wset)
paulson@13833:      apply (rule_tac [2] wset_zcong_prod_1, auto)
wenzelm@11049:   done
paulson@9508: 
paulson@9508: end