--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Algebra/Sylow.thy Tue Mar 18 18:07:06 2003 +0100
@@ -0,0 +1,395 @@
+(* Title: HOL/GroupTheory/Sylow
+ ID: $Id$
+ Author: Florian Kammueller, with new proofs by L C Paulson
+
+See Florian Kamm\"uller and L. C. Paulson,
+ A Formal Proof of Sylow's theorem:
+ An Experiment in Abstract Algebra with Isabelle HOL
+ J. Automated Reasoning 23 (1999), 235-264
+*)
+
+header{*Sylow's theorem using locales*}
+
+theory Sylow = Coset:
+
+subsection {*Order of a Group and Lagrange's Theorem*}
+
+constdefs
+ order :: "(('a,'b) semigroup_scheme) => nat"
+ "order(S) == card(carrier S)"
+
+theorem (in coset) lagrange:
+ "[| finite(carrier G); subgroup H G |]
+ ==> card(rcosets G H) * card(H) = order(G)"
+apply (simp (no_asm_simp) add: order_def setrcos_part_G [symmetric])
+apply (subst mult_commute)
+apply (rule card_partition)
+ apply (simp add: setrcos_subset_PowG [THEN finite_subset])
+ apply (simp add: setrcos_part_G)
+ apply (simp add: card_cosets_equal subgroup.subset)
+apply (simp add: rcos_disjoint)
+done
+
+
+text{*The combinatorial argument is in theory Exponent*}
+
+locale sylow = coset +
+ fixes p and a and m and calM and RelM
+ assumes prime_p: "p \<in> prime"
+ and order_G: "order(G) = (p^a) * m"
+ and finite_G [iff]: "finite (carrier G)"
+ defines "calM == {s. s <= carrier(G) & card(s) = p^a}"
+ and "RelM == {(N1,N2). N1 \<in> calM & N2 \<in> calM &
+ (\<exists>g \<in> carrier(G). N1 = (N2 #> g) )}"
+
+lemma (in sylow) RelM_refl: "refl calM RelM"
+apply (auto simp add: refl_def RelM_def calM_def)
+apply (blast intro!: coset_mult_one [symmetric])
+done
+
+lemma (in sylow) RelM_sym: "sym RelM"
+proof (unfold sym_def RelM_def, clarify)
+ fix y g
+ assume "y \<in> calM"
+ and g: "g \<in> carrier G"
+ hence "y = y #> g #> (inv g)" by (simp add: coset_mult_assoc calM_def)
+ thus "\<exists>g'\<in>carrier G. y = y #> g #> g'"
+ by (blast intro: g inv_closed)
+qed
+
+lemma (in sylow) RelM_trans: "trans RelM"
+by (auto simp add: trans_def RelM_def calM_def coset_mult_assoc)
+
+lemma (in sylow) RelM_equiv: "equiv calM RelM"
+apply (unfold equiv_def)
+apply (blast intro: RelM_refl RelM_sym RelM_trans)
+done
+
+lemma (in sylow) M_subset_calM_prep: "M' \<in> calM // RelM ==> M' <= calM"
+apply (unfold RelM_def)
+apply (blast elim!: quotientE)
+done
+
+subsection{*Main Part of the Proof*}
+
+
+locale sylow_central = sylow +
+ fixes H and M1 and M
+ assumes M_in_quot: "M \<in> calM // RelM"
+ and not_dvd_M: "~(p ^ Suc(exponent p m) dvd card(M))"
+ and M1_in_M: "M1 \<in> M"
+ defines "H == {g. g\<in>carrier G & M1 #> g = M1}"
+
+lemma (in sylow_central) M_subset_calM: "M <= calM"
+by (rule M_in_quot [THEN M_subset_calM_prep])
+
+lemma (in sylow_central) card_M1: "card(M1) = p^a"
+apply (cut_tac M_subset_calM M1_in_M)
+apply (simp add: calM_def, blast)
+done
+
+lemma card_nonempty: "0 < card(S) ==> S \<noteq> {}"
+by force
+
+lemma (in sylow_central) exists_x_in_M1: "\<exists>x. x\<in>M1"
+apply (subgoal_tac "0 < card M1")
+ apply (blast dest: card_nonempty)
+apply (cut_tac prime_p [THEN prime_imp_one_less])
+apply (simp (no_asm_simp) add: card_M1)
+done
+
+lemma (in sylow_central) M1_subset_G [simp]: "M1 <= carrier G"
+apply (rule subsetD [THEN PowD])
+apply (rule_tac [2] M1_in_M)
+apply (rule M_subset_calM [THEN subset_trans])
+apply (auto simp add: calM_def)
+done
+
+lemma (in sylow_central) M1_inj_H: "\<exists>f \<in> H\<rightarrow>M1. inj_on f H"
+ proof -
+ from exists_x_in_M1 obtain m1 where m1M: "m1 \<in> M1"..
+ have m1G: "m1 \<in> carrier G" by (simp add: m1M M1_subset_G [THEN subsetD])
+ show ?thesis
+ proof
+ show "inj_on (\<lambda>z\<in>H. m1 \<otimes> z) H"
+ by (simp add: inj_on_def l_cancel [of m1 x y, THEN iffD1] H_def m1G)
+ show "restrict (op \<otimes> m1) H \<in> H \<rightarrow> M1"
+ proof (rule restrictI)
+ fix z assume zH: "z \<in> H"
+ show "m1 \<otimes> z \<in> M1"
+ proof -
+ from zH
+ have zG: "z \<in> carrier G" and M1zeq: "M1 #> z = M1"
+ by (auto simp add: H_def)
+ show ?thesis
+ by (rule subst [OF M1zeq], simp add: m1M zG rcosI)
+ qed
+ qed
+ qed
+ qed
+
+
+subsection{*Discharging the Assumptions of @{text sylow_central}*}
+
+lemma (in sylow) EmptyNotInEquivSet: "{} \<notin> calM // RelM"
+by (blast elim!: quotientE dest: RelM_equiv [THEN equiv_class_self])
+
+lemma (in sylow) existsM1inM: "M \<in> calM // RelM ==> \<exists>M1. M1 \<in> M"
+apply (subgoal_tac "M \<noteq> {}")
+ apply blast
+apply (cut_tac EmptyNotInEquivSet, blast)
+done
+
+lemma (in sylow) zero_less_o_G: "0 < order(G)"
+apply (unfold order_def)
+apply (blast intro: one_closed zero_less_card_empty)
+done
+
+lemma (in sylow) zero_less_m: "0 < m"
+apply (cut_tac zero_less_o_G)
+apply (simp add: order_G)
+done
+
+lemma (in sylow) card_calM: "card(calM) = (p^a) * m choose p^a"
+by (simp add: calM_def n_subsets order_G [symmetric] order_def)
+
+lemma (in sylow) zero_less_card_calM: "0 < card calM"
+by (simp add: card_calM zero_less_binomial le_extend_mult zero_less_m)
+
+lemma (in sylow) max_p_div_calM:
+ "~ (p ^ Suc(exponent p m) dvd card(calM))"
+apply (subgoal_tac "exponent p m = exponent p (card calM) ")
+ apply (cut_tac zero_less_card_calM prime_p)
+ apply (force dest: power_Suc_exponent_Not_dvd)
+apply (simp add: card_calM zero_less_m [THEN const_p_fac])
+done
+
+lemma (in sylow) finite_calM: "finite calM"
+apply (unfold calM_def)
+apply (rule_tac B = "Pow (carrier G) " in finite_subset)
+apply auto
+done
+
+lemma (in sylow) lemma_A1:
+ "\<exists>M \<in> calM // RelM. ~ (p ^ Suc(exponent p m) dvd card(M))"
+apply (rule max_p_div_calM [THEN contrapos_np])
+apply (simp add: finite_calM equiv_imp_dvd_card [OF _ RelM_equiv])
+done
+
+
+subsubsection{*Introduction and Destruct Rules for @{term H}*}
+
+lemma (in sylow_central) H_I: "[|g \<in> carrier G; M1 #> g = M1|] ==> g \<in> H"
+by (simp add: H_def)
+
+lemma (in sylow_central) H_into_carrier_G: "x \<in> H ==> x \<in> carrier G"
+by (simp add: H_def)
+
+lemma (in sylow_central) in_H_imp_eq: "g : H ==> M1 #> g = M1"
+by (simp add: H_def)
+
+lemma (in sylow_central) H_m_closed: "[| x\<in>H; y\<in>H|] ==> x \<otimes> y \<in> H"
+apply (unfold H_def)
+apply (simp add: coset_mult_assoc [symmetric] m_closed)
+done
+
+lemma (in sylow_central) H_not_empty: "H \<noteq> {}"
+apply (simp add: H_def)
+apply (rule exI [of _ \<one>], simp)
+done
+
+lemma (in sylow_central) H_is_subgroup: "subgroup H G"
+apply (rule subgroupI)
+apply (rule subsetI)
+apply (erule H_into_carrier_G)
+apply (rule H_not_empty)
+apply (simp add: H_def, clarify)
+apply (erule_tac P = "%z. ?lhs(z) = M1" in subst)
+apply (simp add: coset_mult_assoc )
+apply (blast intro: H_m_closed)
+done
+
+
+lemma (in sylow_central) rcosetGM1g_subset_G:
+ "[| g \<in> carrier G; x \<in> M1 #> g |] ==> x \<in> carrier G"
+by (blast intro: M1_subset_G [THEN r_coset_subset_G, THEN subsetD])
+
+lemma (in sylow_central) finite_M1: "finite M1"
+by (rule finite_subset [OF M1_subset_G finite_G])
+
+lemma (in sylow_central) finite_rcosetGM1g: "g\<in>carrier G ==> finite (M1 #> g)"
+apply (rule finite_subset)
+apply (rule subsetI)
+apply (erule rcosetGM1g_subset_G, assumption)
+apply (rule finite_G)
+done
+
+lemma (in sylow_central) M1_cardeq_rcosetGM1g:
+ "g \<in> carrier G ==> card(M1 #> g) = card(M1)"
+by (simp (no_asm_simp) add: M1_subset_G card_cosets_equal setrcosI)
+
+lemma (in sylow_central) M1_RelM_rcosetGM1g:
+ "g \<in> carrier G ==> (M1, M1 #> g) \<in> RelM"
+apply (simp (no_asm) add: RelM_def calM_def card_M1 M1_subset_G)
+apply (rule conjI)
+ apply (blast intro: rcosetGM1g_subset_G)
+apply (simp (no_asm_simp) add: card_M1 M1_cardeq_rcosetGM1g)
+apply (rule bexI [of _ "inv g"])
+apply (simp_all add: coset_mult_assoc M1_subset_G)
+done
+
+
+
+subsection{*Equal Cardinalities of @{term M} and @{term "rcosets G H"}*}
+
+text{*Injections between @{term M} and @{term "rcosets G H"} show that
+ their cardinalities are equal.*}
+
+lemma ElemClassEquiv:
+ "[| equiv A r; C\<in>A // r |] ==> \<forall>x \<in> C. \<forall>y \<in> C. (x,y)\<in>r"
+apply (unfold equiv_def quotient_def sym_def trans_def, blast)
+done
+
+lemma (in sylow_central) M_elem_map:
+ "M2 \<in> M ==> \<exists>g. g \<in> carrier G & M1 #> g = M2"
+apply (cut_tac M1_in_M M_in_quot [THEN RelM_equiv [THEN ElemClassEquiv]])
+apply (simp add: RelM_def)
+apply (blast dest!: bspec)
+done
+
+lemmas (in sylow_central) M_elem_map_carrier =
+ M_elem_map [THEN someI_ex, THEN conjunct1]
+
+lemmas (in sylow_central) M_elem_map_eq =
+ M_elem_map [THEN someI_ex, THEN conjunct2]
+
+lemma (in sylow_central) M_funcset_setrcos_H:
+ "(%x:M. H #> (SOME g. g \<in> carrier G & M1 #> g = x)) \<in> M \<rightarrow> rcosets G H"
+apply (rule setrcosI [THEN restrictI])
+apply (rule H_is_subgroup [THEN subgroup.subset])
+apply (erule M_elem_map_carrier)
+done
+
+lemma (in sylow_central) inj_M_GmodH: "\<exists>f \<in> M\<rightarrow>rcosets G H. inj_on f M"
+apply (rule bexI)
+apply (rule_tac [2] M_funcset_setrcos_H)
+apply (rule inj_onI, simp)
+apply (rule trans [OF _ M_elem_map_eq])
+prefer 2 apply assumption
+apply (rule M_elem_map_eq [symmetric, THEN trans], assumption)
+apply (rule coset_mult_inv1)
+apply (erule_tac [2] M_elem_map_carrier)+
+apply (rule_tac [2] M1_subset_G)
+apply (rule coset_join1 [THEN in_H_imp_eq])
+apply (rule_tac [3] H_is_subgroup)
+prefer 2 apply (blast intro: m_closed M_elem_map_carrier inv_closed)
+apply (simp add: coset_mult_inv2 H_def M_elem_map_carrier subset_def)
+done
+
+
+(** the opposite injection **)
+
+lemma (in sylow_central) H_elem_map:
+ "H1\<in>rcosets G H ==> \<exists>g. g \<in> carrier G & H #> g = H1"
+by (auto simp add: setrcos_eq)
+
+lemmas (in sylow_central) H_elem_map_carrier =
+ H_elem_map [THEN someI_ex, THEN conjunct1]
+
+lemmas (in sylow_central) H_elem_map_eq =
+ H_elem_map [THEN someI_ex, THEN conjunct2]
+
+
+lemma EquivElemClass:
+ "[|equiv A r; M\<in>A // r; M1\<in>M; (M1, M2)\<in>r |] ==> M2\<in>M"
+apply (unfold equiv_def quotient_def sym_def trans_def, blast)
+done
+
+lemma (in sylow_central) setrcos_H_funcset_M:
+ "(\<lambda>C \<in> rcosets G H. M1 #> (@g. g \<in> carrier G \<and> H #> g = C))
+ \<in> rcosets G H \<rightarrow> M"
+apply (simp add: setrcos_eq)
+apply (fast intro: someI2
+ intro!: restrictI M1_in_M
+ EquivElemClass [OF RelM_equiv M_in_quot _ M1_RelM_rcosetGM1g])
+done
+
+text{*close to a duplicate of @{text inj_M_GmodH}*}
+lemma (in sylow_central) inj_GmodH_M:
+ "\<exists>g \<in> rcosets G H\<rightarrow>M. inj_on g (rcosets G H)"
+apply (rule bexI)
+apply (rule_tac [2] setrcos_H_funcset_M)
+apply (rule inj_onI)
+apply (simp)
+apply (rule trans [OF _ H_elem_map_eq])
+prefer 2 apply assumption
+apply (rule H_elem_map_eq [symmetric, THEN trans], assumption)
+apply (rule coset_mult_inv1)
+apply (erule_tac [2] H_elem_map_carrier)+
+apply (rule_tac [2] H_is_subgroup [THEN subgroup.subset])
+apply (rule coset_join2)
+apply (blast intro: m_closed inv_closed H_elem_map_carrier)
+apply (rule H_is_subgroup)
+apply (simp add: H_I coset_mult_inv2 M1_subset_G H_elem_map_carrier)
+done
+
+lemma (in sylow_central) calM_subset_PowG: "calM <= Pow(carrier G)"
+by (auto simp add: calM_def)
+
+
+lemma (in sylow_central) finite_M: "finite M"
+apply (rule finite_subset)
+apply (rule M_subset_calM [THEN subset_trans])
+apply (rule calM_subset_PowG, blast)
+done
+
+lemma (in sylow_central) cardMeqIndexH: "card(M) = card(rcosets G H)"
+apply (insert inj_M_GmodH inj_GmodH_M)
+apply (blast intro: card_bij finite_M H_is_subgroup
+ setrcos_subset_PowG [THEN finite_subset]
+ finite_Pow_iff [THEN iffD2])
+done
+
+lemma (in sylow_central) index_lem: "card(M) * card(H) = order(G)"
+by (simp add: cardMeqIndexH lagrange H_is_subgroup)
+
+lemma (in sylow_central) lemma_leq1: "p^a <= card(H)"
+apply (rule dvd_imp_le)
+ apply (rule div_combine [OF prime_p not_dvd_M])
+ prefer 2 apply (blast intro: subgroup.finite_imp_card_positive H_is_subgroup)
+apply (simp add: index_lem order_G power_add mult_dvd_mono power_exponent_dvd
+ zero_less_m)
+done
+
+lemma (in sylow_central) lemma_leq2: "card(H) <= p^a"
+apply (subst card_M1 [symmetric])
+apply (cut_tac M1_inj_H)
+apply (blast intro!: M1_subset_G intro:
+ card_inj H_into_carrier_G finite_subset [OF _ finite_G])
+done
+
+lemma (in sylow_central) card_H_eq: "card(H) = p^a"
+by (blast intro: le_anti_sym lemma_leq1 lemma_leq2)
+
+lemma (in sylow) sylow_thm: "\<exists>H. subgroup H G & card(H) = p^a"
+apply (cut_tac lemma_A1, clarify)
+apply (frule existsM1inM, clarify)
+apply (subgoal_tac "sylow_central G p a m M1 M")
+ apply (blast dest: sylow_central.H_is_subgroup sylow_central.card_H_eq)
+apply (simp add: sylow_central_def sylow_central_axioms_def prems)
+done
+
+text{*Needed because the locale's automatic definition refers to
+ @{term "semigroup G"} and @{term "group_axioms G"} rather than
+ simply to @{term "group G"}.*}
+lemma sylow_eq: "sylow G p a m = (group G & sylow_axioms G p a m)"
+by (simp add: sylow_def group_def)
+
+theorem sylow_thm:
+ "[|p \<in> prime; group(G); order(G) = (p^a) * m; finite (carrier G)|]
+ ==> \<exists>H. subgroup H G & card(H) = p^a"
+apply (rule sylow.sylow_thm [of G p a m])
+apply (simp add: sylow_eq sylow_axioms_def)
+done
+
+end