src/HOL/Algebra/AbelCoset.thy
author ballarin
Tue Jul 15 16:50:09 2008 +0200 (2008-07-15)
changeset 27611 2c01c0bdb385
parent 27192 005d4b953fdc
child 27717 21bbd410ba04
permissions -rw-r--r--
Removed uses of context element includes.
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(*
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  Title:     HOL/Algebra/AbelCoset.thy
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  Id:        $Id$
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  Author:    Stephan Hohe, TU Muenchen
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*)
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theory AbelCoset
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imports Coset Ring
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begin
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section {* More Lifting from Groups to Abelian Groups *}
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subsection {* Definitions *}
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text {* Hiding @{text "<+>"} from @{theory Sum_Type} until I come
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  up with better syntax here *}
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no_notation Plus (infixr "<+>" 65)
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constdefs (structure G)
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  a_r_coset    :: "[_, 'a set, 'a] \<Rightarrow> 'a set"    (infixl "+>\<index>" 60)
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  "a_r_coset G \<equiv> r_coset \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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  a_l_coset    :: "[_, 'a, 'a set] \<Rightarrow> 'a set"    (infixl "<+\<index>" 60)
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  "a_l_coset G \<equiv> l_coset \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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  A_RCOSETS  :: "[_, 'a set] \<Rightarrow> ('a set)set"   ("a'_rcosets\<index> _" [81] 80)
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  "A_RCOSETS G H \<equiv> RCOSETS \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> H"
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  set_add  :: "[_, 'a set ,'a set] \<Rightarrow> 'a set" (infixl "<+>\<index>" 60)
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  "set_add G \<equiv> set_mult \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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  A_SET_INV :: "[_,'a set] \<Rightarrow> 'a set"  ("a'_set'_inv\<index> _" [81] 80)
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  "A_SET_INV G H \<equiv> SET_INV \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> H"
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constdefs (structure G)
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  a_r_congruent :: "[('a,'b)ring_scheme, 'a set] \<Rightarrow> ('a*'a)set"
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                  ("racong\<index> _")
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   "a_r_congruent G \<equiv> r_congruent \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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constdefs
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  A_FactGroup :: "[('a,'b) ring_scheme, 'a set] \<Rightarrow> ('a set) monoid"
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     (infixl "A'_Mod" 65)
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    --{*Actually defined for groups rather than monoids*}
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  "A_FactGroup G H \<equiv> FactGroup \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> H"
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constdefs
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  a_kernel :: "('a, 'm) ring_scheme \<Rightarrow> ('b, 'n) ring_scheme \<Rightarrow> 
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             ('a \<Rightarrow> 'b) \<Rightarrow> 'a set" 
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    --{*the kernel of a homomorphism (additive)*}
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  "a_kernel G H h \<equiv> kernel \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>
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                              \<lparr>carrier = carrier H, mult = add H, one = zero H\<rparr> h"
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locale abelian_group_hom = abelian_group G + abelian_group H + var h +
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  assumes a_group_hom: "group_hom (| carrier = carrier G, mult = add G, one = zero G |)
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                                  (| carrier = carrier H, mult = add H, one = zero H |) h"
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lemmas a_r_coset_defs =
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  a_r_coset_def r_coset_def
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lemma a_r_coset_def':
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  fixes G (structure)
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  shows "H +> a \<equiv> \<Union>h\<in>H. {h \<oplus> a}"
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unfolding a_r_coset_defs
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by simp
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lemmas a_l_coset_defs =
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  a_l_coset_def l_coset_def
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lemma a_l_coset_def':
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  fixes G (structure)
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  shows "a <+ H \<equiv> \<Union>h\<in>H. {a \<oplus> h}"
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unfolding a_l_coset_defs
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by simp
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lemmas A_RCOSETS_defs =
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  A_RCOSETS_def RCOSETS_def
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lemma A_RCOSETS_def':
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  fixes G (structure)
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  shows "a_rcosets H \<equiv> \<Union>a\<in>carrier G. {H +> a}"
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unfolding A_RCOSETS_defs
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by (fold a_r_coset_def, simp)
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lemmas set_add_defs =
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  set_add_def set_mult_def
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lemma set_add_def':
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  fixes G (structure)
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  shows "H <+> K \<equiv> \<Union>h\<in>H. \<Union>k\<in>K. {h \<oplus> k}"
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unfolding set_add_defs
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by simp
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lemmas A_SET_INV_defs =
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  A_SET_INV_def SET_INV_def
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lemma A_SET_INV_def':
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  fixes G (structure)
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  shows "a_set_inv H \<equiv> \<Union>h\<in>H. {\<ominus> h}"
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unfolding A_SET_INV_defs
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by (fold a_inv_def)
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subsection {* Cosets *}
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lemma (in abelian_group) a_coset_add_assoc:
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     "[| M \<subseteq> carrier G; g \<in> carrier G; h \<in> carrier G |]
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      ==> (M +> g) +> h = M +> (g \<oplus> h)"
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by (rule group.coset_mult_assoc [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_coset_add_zero [simp]:
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  "M \<subseteq> carrier G ==> M +> \<zero> = M"
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by (rule group.coset_mult_one [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_coset_add_inv1:
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     "[| M +> (x \<oplus> (\<ominus> y)) = M;  x \<in> carrier G ; y \<in> carrier G;
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         M \<subseteq> carrier G |] ==> M +> x = M +> y"
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by (rule group.coset_mult_inv1 [OF a_group,
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    folded a_r_coset_def a_inv_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_coset_add_inv2:
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     "[| M +> x = M +> y;  x \<in> carrier G;  y \<in> carrier G;  M \<subseteq> carrier G |]
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      ==> M +> (x \<oplus> (\<ominus> y)) = M"
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by (rule group.coset_mult_inv2 [OF a_group,
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    folded a_r_coset_def a_inv_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_coset_join1:
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     "[| H +> x = H;  x \<in> carrier G;  subgroup H (|carrier = carrier G, mult = add G, one = zero G|) |] ==> x \<in> H"
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by (rule group.coset_join1 [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_solve_equation:
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    "\<lbrakk>subgroup H (|carrier = carrier G, mult = add G, one = zero G|); x \<in> H; y \<in> H\<rbrakk> \<Longrightarrow> \<exists>h\<in>H. y = h \<oplus> x"
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by (rule group.solve_equation [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_repr_independence:
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     "\<lbrakk>y \<in> H +> x;  x \<in> carrier G; subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> \<rbrakk> \<Longrightarrow> H +> x = H +> y"
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by (rule group.repr_independence [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_coset_join2:
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     "\<lbrakk>x \<in> carrier G;  subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>; x\<in>H\<rbrakk> \<Longrightarrow> H +> x = H"
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by (rule group.coset_join2 [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_monoid) a_r_coset_subset_G:
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     "[| H \<subseteq> carrier G; x \<in> carrier G |] ==> H +> x \<subseteq> carrier G"
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by (rule monoid.r_coset_subset_G [OF a_monoid,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_rcosI:
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     "[| h \<in> H; H \<subseteq> carrier G; x \<in> carrier G|] ==> h \<oplus> x \<in> H +> x"
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by (rule group.rcosI [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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lemma (in abelian_group) a_rcosetsI:
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     "\<lbrakk>H \<subseteq> carrier G; x \<in> carrier G\<rbrakk> \<Longrightarrow> H +> x \<in> a_rcosets H"
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by (rule group.rcosetsI [OF a_group,
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    folded a_r_coset_def A_RCOSETS_def, simplified monoid_record_simps])
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text{*Really needed?*}
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lemma (in abelian_group) a_transpose_inv:
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     "[| x \<oplus> y = z;  x \<in> carrier G;  y \<in> carrier G;  z \<in> carrier G |]
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      ==> (\<ominus> x) \<oplus> z = y"
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by (rule group.transpose_inv [OF a_group,
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    folded a_r_coset_def a_inv_def, simplified monoid_record_simps])
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(*
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--"duplicate"
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lemma (in abelian_group) a_rcos_self:
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     "[| x \<in> carrier G; subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> |] ==> x \<in> H +> x"
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by (rule group.rcos_self [OF a_group,
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    folded a_r_coset_def, simplified monoid_record_simps])
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*)
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subsection {* Subgroups *}
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locale additive_subgroup = var H + struct G +
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  assumes a_subgroup: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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lemma (in additive_subgroup) is_additive_subgroup:
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  shows "additive_subgroup H G"
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by (rule additive_subgroup_axioms)
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lemma additive_subgroupI:
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  fixes G (structure)
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  assumes a_subgroup: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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  shows "additive_subgroup H G"
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by (rule additive_subgroup.intro) (rule a_subgroup)
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lemma (in additive_subgroup) a_subset:
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     "H \<subseteq> carrier G"
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by (rule subgroup.subset[OF a_subgroup,
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    simplified monoid_record_simps])
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lemma (in additive_subgroup) a_closed [intro, simp]:
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     "\<lbrakk>x \<in> H; y \<in> H\<rbrakk> \<Longrightarrow> x \<oplus> y \<in> H"
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by (rule subgroup.m_closed[OF a_subgroup,
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    simplified monoid_record_simps])
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lemma (in additive_subgroup) zero_closed [simp]:
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     "\<zero> \<in> H"
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by (rule subgroup.one_closed[OF a_subgroup,
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    simplified monoid_record_simps])
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lemma (in additive_subgroup) a_inv_closed [intro,simp]:
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     "x \<in> H \<Longrightarrow> \<ominus> x \<in> H"
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by (rule subgroup.m_inv_closed[OF a_subgroup,
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    folded a_inv_def, simplified monoid_record_simps])
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subsection {* Normal additive subgroups *}
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subsubsection {* Definition of @{text "abelian_subgroup"} *}
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text {* Every subgroup of an @{text "abelian_group"} is normal *}
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locale abelian_subgroup = additive_subgroup H G + abelian_group G +
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  assumes a_normal: "normal H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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lemma (in abelian_subgroup) is_abelian_subgroup:
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  shows "abelian_subgroup H G"
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by (rule abelian_subgroup_axioms)
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lemma abelian_subgroupI:
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  assumes a_normal: "normal H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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      and a_comm: "!!x y. [| x \<in> carrier G; y \<in> carrier G |] ==> x \<oplus>\<^bsub>G\<^esub> y = y \<oplus>\<^bsub>G\<^esub> x"
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  shows "abelian_subgroup H G"
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proof -
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  interpret normal ["H" "\<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"]
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  by (rule a_normal)
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  show "abelian_subgroup H G"
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  by (unfold_locales, simp add: a_comm)
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qed
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lemma abelian_subgroupI2:
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  fixes G (structure)
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  assumes a_comm_group: "comm_group \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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      and a_subgroup: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
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  shows "abelian_subgroup H G"
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proof -
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  interpret comm_group ["\<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"]
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  by (rule a_comm_group)
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  interpret subgroup ["H" "\<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"]
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  by (rule a_subgroup)
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  show "abelian_subgroup H G"
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  apply unfold_locales
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  proof (simp add: r_coset_def l_coset_def, clarsimp)
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    fix x
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    assume xcarr: "x \<in> carrier G"
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    from a_subgroup
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        have Hcarr: "H \<subseteq> carrier G" by (unfold subgroup_def, simp)
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    from xcarr Hcarr
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        show "(\<Union>h\<in>H. {h \<oplus>\<^bsub>G\<^esub> x}) = (\<Union>h\<in>H. {x \<oplus>\<^bsub>G\<^esub> h})"
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        using m_comm[simplified]
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        by fast
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  qed
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qed
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lemma abelian_subgroupI3:
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  fixes G (structure)
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  assumes asg: "additive_subgroup H G"
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      and ag: "abelian_group G"
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  shows "abelian_subgroup H G"
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apply (rule abelian_subgroupI2)
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 apply (rule abelian_group.a_comm_group[OF ag])
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apply (rule additive_subgroup.a_subgroup[OF asg])
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done
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lemma (in abelian_subgroup) a_coset_eq:
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     "(\<forall>x \<in> carrier G. H +> x = x <+ H)"
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by (rule normal.coset_eq[OF a_normal,
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    folded a_r_coset_def a_l_coset_def, simplified monoid_record_simps])
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lemma (in abelian_subgroup) a_inv_op_closed1:
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  shows "\<lbrakk>x \<in> carrier G; h \<in> H\<rbrakk> \<Longrightarrow> (\<ominus> x) \<oplus> h \<oplus> x \<in> H"
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by (rule normal.inv_op_closed1 [OF a_normal,
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    folded a_inv_def, simplified monoid_record_simps])
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lemma (in abelian_subgroup) a_inv_op_closed2:
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  shows "\<lbrakk>x \<in> carrier G; h \<in> H\<rbrakk> \<Longrightarrow> x \<oplus> h \<oplus> (\<ominus> x) \<in> H"
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by (rule normal.inv_op_closed2 [OF a_normal,
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    folded a_inv_def, simplified monoid_record_simps])
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text{*Alternative characterization of normal subgroups*}
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lemma (in abelian_group) a_normal_inv_iff:
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     "(N \<lhd> \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>) = 
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      (subgroup N \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> & (\<forall>x \<in> carrier G. \<forall>h \<in> N. x \<oplus> h \<oplus> (\<ominus> x) \<in> N))"
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      (is "_ = ?rhs")
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by (rule group.normal_inv_iff [OF a_group,
ballarin@20318
   298
    folded a_inv_def, simplified monoid_record_simps])
ballarin@20318
   299
ballarin@20318
   300
lemma (in abelian_group) a_lcos_m_assoc:
ballarin@20318
   301
     "[| M \<subseteq> carrier G; g \<in> carrier G; h \<in> carrier G |]
ballarin@20318
   302
      ==> g <+ (h <+ M) = (g \<oplus> h) <+ M"
ballarin@20318
   303
by (rule group.lcos_m_assoc [OF a_group,
ballarin@20318
   304
    folded a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   305
ballarin@20318
   306
lemma (in abelian_group) a_lcos_mult_one:
ballarin@20318
   307
     "M \<subseteq> carrier G ==> \<zero> <+ M = M"
ballarin@20318
   308
by (rule group.lcos_mult_one [OF a_group,
ballarin@20318
   309
    folded a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   310
ballarin@20318
   311
ballarin@20318
   312
lemma (in abelian_group) a_l_coset_subset_G:
ballarin@20318
   313
     "[| H \<subseteq> carrier G; x \<in> carrier G |] ==> x <+ H \<subseteq> carrier G"
ballarin@20318
   314
by (rule group.l_coset_subset_G [OF a_group,
ballarin@20318
   315
    folded a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   316
ballarin@20318
   317
ballarin@20318
   318
lemma (in abelian_group) a_l_coset_swap:
ballarin@20318
   319
     "\<lbrakk>y \<in> x <+ H;  x \<in> carrier G;  subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>\<rbrakk> \<Longrightarrow> x \<in> y <+ H"
ballarin@20318
   320
by (rule group.l_coset_swap [OF a_group,
ballarin@20318
   321
    folded a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   322
ballarin@20318
   323
lemma (in abelian_group) a_l_coset_carrier:
ballarin@20318
   324
     "[| y \<in> x <+ H;  x \<in> carrier G;  subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> |] ==> y \<in> carrier G"
ballarin@20318
   325
by (rule group.l_coset_carrier [OF a_group,
ballarin@20318
   326
    folded a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   327
ballarin@20318
   328
lemma (in abelian_group) a_l_repr_imp_subset:
ballarin@20318
   329
  assumes y: "y \<in> x <+ H" and x: "x \<in> carrier G" and sb: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
ballarin@20318
   330
  shows "y <+ H \<subseteq> x <+ H"
wenzelm@23350
   331
apply (rule group.l_repr_imp_subset [OF a_group,
ballarin@20318
   332
    folded a_l_coset_def, simplified monoid_record_simps])
wenzelm@23350
   333
apply (rule y)
wenzelm@23350
   334
apply (rule x)
wenzelm@23350
   335
apply (rule sb)
wenzelm@23350
   336
done
ballarin@20318
   337
ballarin@20318
   338
lemma (in abelian_group) a_l_repr_independence:
ballarin@20318
   339
  assumes y: "y \<in> x <+ H" and x: "x \<in> carrier G" and sb: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr>"
ballarin@20318
   340
  shows "x <+ H = y <+ H"
wenzelm@23350
   341
apply (rule group.l_repr_independence [OF a_group,
ballarin@20318
   342
    folded a_l_coset_def, simplified monoid_record_simps])
wenzelm@23350
   343
apply (rule y)
wenzelm@23350
   344
apply (rule x)
wenzelm@23350
   345
apply (rule sb)
wenzelm@23350
   346
done
ballarin@20318
   347
ballarin@20318
   348
lemma (in abelian_group) setadd_subset_G:
ballarin@20318
   349
     "\<lbrakk>H \<subseteq> carrier G; K \<subseteq> carrier G\<rbrakk> \<Longrightarrow> H <+> K \<subseteq> carrier G"
ballarin@20318
   350
by (rule group.setmult_subset_G [OF a_group,
ballarin@20318
   351
    folded set_add_def, simplified monoid_record_simps])
ballarin@20318
   352
ballarin@20318
   353
lemma (in abelian_group) subgroup_add_id: "subgroup H \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> \<Longrightarrow> H <+> H = H"
ballarin@20318
   354
by (rule group.subgroup_mult_id [OF a_group,
ballarin@20318
   355
    folded set_add_def, simplified monoid_record_simps])
ballarin@20318
   356
ballarin@20318
   357
lemma (in abelian_subgroup) a_rcos_inv:
ballarin@20318
   358
  assumes x:     "x \<in> carrier G"
ballarin@20318
   359
  shows "a_set_inv (H +> x) = H +> (\<ominus> x)" 
ballarin@20318
   360
by (rule normal.rcos_inv [OF a_normal,
wenzelm@23350
   361
  folded a_r_coset_def a_inv_def A_SET_INV_def, simplified monoid_record_simps]) (rule x)
ballarin@20318
   362
ballarin@20318
   363
lemma (in abelian_group) a_setmult_rcos_assoc:
ballarin@20318
   364
     "\<lbrakk>H \<subseteq> carrier G; K \<subseteq> carrier G; x \<in> carrier G\<rbrakk>
ballarin@20318
   365
      \<Longrightarrow> H <+> (K +> x) = (H <+> K) +> x"
ballarin@20318
   366
by (rule group.setmult_rcos_assoc [OF a_group,
ballarin@20318
   367
    folded set_add_def a_r_coset_def, simplified monoid_record_simps])
ballarin@20318
   368
ballarin@20318
   369
lemma (in abelian_group) a_rcos_assoc_lcos:
ballarin@20318
   370
     "\<lbrakk>H \<subseteq> carrier G; K \<subseteq> carrier G; x \<in> carrier G\<rbrakk>
ballarin@20318
   371
      \<Longrightarrow> (H +> x) <+> K = H <+> (x <+ K)"
ballarin@20318
   372
by (rule group.rcos_assoc_lcos [OF a_group,
ballarin@20318
   373
     folded set_add_def a_r_coset_def a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   374
ballarin@20318
   375
lemma (in abelian_subgroup) a_rcos_sum:
ballarin@20318
   376
     "\<lbrakk>x \<in> carrier G; y \<in> carrier G\<rbrakk>
ballarin@20318
   377
      \<Longrightarrow> (H +> x) <+> (H +> y) = H +> (x \<oplus> y)"
ballarin@20318
   378
by (rule normal.rcos_sum [OF a_normal,
ballarin@20318
   379
    folded set_add_def a_r_coset_def, simplified monoid_record_simps])
ballarin@20318
   380
ballarin@20318
   381
lemma (in abelian_subgroup) rcosets_add_eq:
ballarin@20318
   382
  "M \<in> a_rcosets H \<Longrightarrow> H <+> M = M"
ballarin@20318
   383
  -- {* generalizes @{text subgroup_mult_id} *}
ballarin@20318
   384
by (rule normal.rcosets_mult_eq [OF a_normal,
ballarin@20318
   385
    folded set_add_def A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   386
ballarin@20318
   387
ballarin@20318
   388
subsection {* Congruence Relation *}
ballarin@20318
   389
ballarin@20318
   390
lemma (in abelian_subgroup) a_equiv_rcong:
ballarin@20318
   391
   shows "equiv (carrier G) (racong H)"
ballarin@20318
   392
by (rule subgroup.equiv_rcong [OF a_subgroup a_group,
ballarin@20318
   393
    folded a_r_congruent_def, simplified monoid_record_simps])
ballarin@20318
   394
ballarin@20318
   395
lemma (in abelian_subgroup) a_l_coset_eq_rcong:
ballarin@20318
   396
  assumes a: "a \<in> carrier G"
ballarin@20318
   397
  shows "a <+ H = racong H `` {a}"
ballarin@20318
   398
by (rule subgroup.l_coset_eq_rcong [OF a_subgroup a_group,
wenzelm@23350
   399
    folded a_r_congruent_def a_l_coset_def, simplified monoid_record_simps]) (rule a)
ballarin@20318
   400
ballarin@20318
   401
lemma (in abelian_subgroup) a_rcos_equation:
ballarin@20318
   402
  shows
ballarin@20318
   403
     "\<lbrakk>ha \<oplus> a = h \<oplus> b; a \<in> carrier G;  b \<in> carrier G;  
ballarin@20318
   404
        h \<in> H;  ha \<in> H;  hb \<in> H\<rbrakk>
ballarin@20318
   405
      \<Longrightarrow> hb \<oplus> a \<in> (\<Union>h\<in>H. {h \<oplus> b})"
ballarin@20318
   406
by (rule group.rcos_equation [OF a_group a_subgroup,
ballarin@20318
   407
    folded a_r_congruent_def a_l_coset_def, simplified monoid_record_simps])
ballarin@20318
   408
ballarin@20318
   409
lemma (in abelian_subgroup) a_rcos_disjoint:
ballarin@20318
   410
  shows "\<lbrakk>a \<in> a_rcosets H; b \<in> a_rcosets H; a\<noteq>b\<rbrakk> \<Longrightarrow> a \<inter> b = {}"
ballarin@20318
   411
by (rule group.rcos_disjoint [OF a_group a_subgroup,
ballarin@20318
   412
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   413
ballarin@20318
   414
lemma (in abelian_subgroup) a_rcos_self:
ballarin@20318
   415
  shows "x \<in> carrier G \<Longrightarrow> x \<in> H +> x"
wenzelm@26310
   416
by (rule group.rcos_self [OF a_group _ a_subgroup,
ballarin@20318
   417
    folded a_r_coset_def, simplified monoid_record_simps])
ballarin@20318
   418
ballarin@20318
   419
lemma (in abelian_subgroup) a_rcosets_part_G:
ballarin@20318
   420
  shows "\<Union>(a_rcosets H) = carrier G"
ballarin@20318
   421
by (rule group.rcosets_part_G [OF a_group a_subgroup,
ballarin@20318
   422
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   423
ballarin@20318
   424
lemma (in abelian_subgroup) a_cosets_finite:
ballarin@20318
   425
     "\<lbrakk>c \<in> a_rcosets H;  H \<subseteq> carrier G;  finite (carrier G)\<rbrakk> \<Longrightarrow> finite c"
ballarin@20318
   426
by (rule group.cosets_finite [OF a_group,
ballarin@20318
   427
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   428
ballarin@20318
   429
lemma (in abelian_group) a_card_cosets_equal:
ballarin@20318
   430
     "\<lbrakk>c \<in> a_rcosets H;  H \<subseteq> carrier G; finite(carrier G)\<rbrakk>
ballarin@20318
   431
      \<Longrightarrow> card c = card H"
ballarin@20318
   432
by (rule group.card_cosets_equal [OF a_group,
ballarin@20318
   433
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   434
ballarin@20318
   435
lemma (in abelian_group) rcosets_subset_PowG:
ballarin@20318
   436
     "additive_subgroup H G  \<Longrightarrow> a_rcosets H \<subseteq> Pow(carrier G)"
ballarin@20318
   437
by (rule group.rcosets_subset_PowG [OF a_group,
ballarin@20318
   438
    folded A_RCOSETS_def, simplified monoid_record_simps],
ballarin@20318
   439
    rule additive_subgroup.a_subgroup)
ballarin@20318
   440
ballarin@20318
   441
theorem (in abelian_group) a_lagrange:
ballarin@20318
   442
     "\<lbrakk>finite(carrier G); additive_subgroup H G\<rbrakk>
ballarin@20318
   443
      \<Longrightarrow> card(a_rcosets H) * card(H) = order(G)"
ballarin@20318
   444
by (rule group.lagrange [OF a_group,
ballarin@20318
   445
    folded A_RCOSETS_def, simplified monoid_record_simps order_def, folded order_def])
ballarin@20318
   446
    (fast intro!: additive_subgroup.a_subgroup)+
ballarin@20318
   447
ballarin@20318
   448
ballarin@20318
   449
subsection {* Factorization *}
ballarin@20318
   450
ballarin@20318
   451
lemmas A_FactGroup_defs = A_FactGroup_def FactGroup_def
ballarin@20318
   452
ballarin@20318
   453
lemma A_FactGroup_def':
ballarin@27611
   454
  fixes G (structure)
ballarin@20318
   455
  shows "G A_Mod H \<equiv> \<lparr>carrier = a_rcosets\<^bsub>G\<^esub> H, mult = set_add G, one = H\<rparr>"
ballarin@20318
   456
unfolding A_FactGroup_defs
ballarin@20318
   457
by (fold A_RCOSETS_def set_add_def)
ballarin@20318
   458
ballarin@20318
   459
ballarin@20318
   460
lemma (in abelian_subgroup) a_setmult_closed:
ballarin@20318
   461
     "\<lbrakk>K1 \<in> a_rcosets H; K2 \<in> a_rcosets H\<rbrakk> \<Longrightarrow> K1 <+> K2 \<in> a_rcosets H"
ballarin@20318
   462
by (rule normal.setmult_closed [OF a_normal,
ballarin@20318
   463
    folded A_RCOSETS_def set_add_def, simplified monoid_record_simps])
ballarin@20318
   464
ballarin@20318
   465
lemma (in abelian_subgroup) a_setinv_closed:
ballarin@20318
   466
     "K \<in> a_rcosets H \<Longrightarrow> a_set_inv K \<in> a_rcosets H"
ballarin@20318
   467
by (rule normal.setinv_closed [OF a_normal,
ballarin@20318
   468
    folded A_RCOSETS_def A_SET_INV_def, simplified monoid_record_simps])
ballarin@20318
   469
ballarin@20318
   470
lemma (in abelian_subgroup) a_rcosets_assoc:
ballarin@20318
   471
     "\<lbrakk>M1 \<in> a_rcosets H; M2 \<in> a_rcosets H; M3 \<in> a_rcosets H\<rbrakk>
ballarin@20318
   472
      \<Longrightarrow> M1 <+> M2 <+> M3 = M1 <+> (M2 <+> M3)"
ballarin@20318
   473
by (rule normal.rcosets_assoc [OF a_normal,
ballarin@20318
   474
    folded A_RCOSETS_def set_add_def, simplified monoid_record_simps])
ballarin@20318
   475
ballarin@20318
   476
lemma (in abelian_subgroup) a_subgroup_in_rcosets:
ballarin@20318
   477
     "H \<in> a_rcosets H"
ballarin@20318
   478
by (rule subgroup.subgroup_in_rcosets [OF a_subgroup a_group,
ballarin@20318
   479
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   480
ballarin@20318
   481
lemma (in abelian_subgroup) a_rcosets_inv_mult_group_eq:
ballarin@20318
   482
     "M \<in> a_rcosets H \<Longrightarrow> a_set_inv M <+> M = H"
ballarin@20318
   483
by (rule normal.rcosets_inv_mult_group_eq [OF a_normal,
ballarin@20318
   484
    folded A_RCOSETS_def A_SET_INV_def set_add_def, simplified monoid_record_simps])
ballarin@20318
   485
ballarin@20318
   486
theorem (in abelian_subgroup) a_factorgroup_is_group:
ballarin@20318
   487
  "group (G A_Mod H)"
ballarin@20318
   488
by (rule normal.factorgroup_is_group [OF a_normal,
ballarin@20318
   489
    folded A_FactGroup_def, simplified monoid_record_simps])
ballarin@20318
   490
ballarin@20318
   491
text {* Since the Factorization is based on an \emph{abelian} subgroup, is results in 
ballarin@20318
   492
        a commutative group *}
ballarin@20318
   493
theorem (in abelian_subgroup) a_factorgroup_is_comm_group:
ballarin@20318
   494
  "comm_group (G A_Mod H)"
ballarin@20318
   495
apply (intro comm_group.intro comm_monoid.intro) prefer 3
ballarin@20318
   496
  apply (rule a_factorgroup_is_group)
ballarin@20318
   497
 apply (rule group.axioms[OF a_factorgroup_is_group])
ballarin@20318
   498
apply (rule comm_monoid_axioms.intro)
ballarin@20318
   499
apply (unfold A_FactGroup_def FactGroup_def RCOSETS_def, fold set_add_def a_r_coset_def, clarsimp)
ballarin@20318
   500
apply (simp add: a_rcos_sum a_comm)
ballarin@20318
   501
done
ballarin@20318
   502
ballarin@20318
   503
lemma add_A_FactGroup [simp]: "X \<otimes>\<^bsub>(G A_Mod H)\<^esub> X' = X <+>\<^bsub>G\<^esub> X'"
ballarin@20318
   504
by (simp add: A_FactGroup_def set_add_def)
ballarin@20318
   505
ballarin@20318
   506
lemma (in abelian_subgroup) a_inv_FactGroup:
ballarin@20318
   507
     "X \<in> carrier (G A_Mod H) \<Longrightarrow> inv\<^bsub>G A_Mod H\<^esub> X = a_set_inv X"
ballarin@20318
   508
by (rule normal.inv_FactGroup [OF a_normal,
ballarin@20318
   509
    folded A_FactGroup_def A_SET_INV_def, simplified monoid_record_simps])
ballarin@20318
   510
ballarin@20318
   511
text{*The coset map is a homomorphism from @{term G} to the quotient group
ballarin@20318
   512
  @{term "G Mod H"}*}
ballarin@20318
   513
lemma (in abelian_subgroup) a_r_coset_hom_A_Mod:
ballarin@20318
   514
  "(\<lambda>a. H +> a) \<in> hom \<lparr>carrier = carrier G, mult = add G, one = zero G\<rparr> (G A_Mod H)"
ballarin@20318
   515
by (rule normal.r_coset_hom_Mod [OF a_normal,
ballarin@20318
   516
    folded A_FactGroup_def a_r_coset_def, simplified monoid_record_simps])
ballarin@20318
   517
ballarin@20318
   518
text {* The isomorphism theorems have been omitted from lifting, at
ballarin@20318
   519
  least for now *}
ballarin@20318
   520
ballarin@20318
   521
subsection{*The First Isomorphism Theorem*}
ballarin@20318
   522
ballarin@20318
   523
text{*The quotient by the kernel of a homomorphism is isomorphic to the 
ballarin@20318
   524
  range of that homomorphism.*}
ballarin@20318
   525
ballarin@20318
   526
lemmas a_kernel_defs =
ballarin@20318
   527
  a_kernel_def kernel_def
ballarin@20318
   528
ballarin@20318
   529
lemma a_kernel_def':
ballarin@20318
   530
  "a_kernel R S h \<equiv> {x \<in> carrier R. h x = \<zero>\<^bsub>S\<^esub>}"
ballarin@20318
   531
by (rule a_kernel_def[unfolded kernel_def, simplified ring_record_simps])
ballarin@20318
   532
ballarin@20318
   533
ballarin@20318
   534
subsection {* Homomorphisms *}
ballarin@20318
   535
ballarin@20318
   536
lemma abelian_group_homI:
ballarin@27611
   537
  assumes "abelian_group G"
ballarin@27611
   538
  assumes "abelian_group H"
ballarin@20318
   539
  assumes a_group_hom: "group_hom (| carrier = carrier G, mult = add G, one = zero G |)
ballarin@20318
   540
                                  (| carrier = carrier H, mult = add H, one = zero H |) h"
ballarin@20318
   541
  shows "abelian_group_hom G H h"
ballarin@27611
   542
proof -
ballarin@27611
   543
  interpret G: abelian_group [G] by fact
ballarin@27611
   544
  interpret H: abelian_group [H] by fact
ballarin@27611
   545
  show ?thesis apply (intro abelian_group_hom.intro abelian_group_hom_axioms.intro)
ballarin@27611
   546
    apply fact
ballarin@27611
   547
    apply fact
ballarin@27611
   548
    apply (rule a_group_hom)
ballarin@27611
   549
    done
ballarin@27611
   550
qed
ballarin@20318
   551
ballarin@20318
   552
lemma (in abelian_group_hom) is_abelian_group_hom:
ballarin@20318
   553
  "abelian_group_hom G H h"
ballarin@20318
   554
by (unfold_locales)
ballarin@20318
   555
ballarin@20318
   556
lemma (in abelian_group_hom) hom_add [simp]:
ballarin@20318
   557
  "[| x : carrier G; y : carrier G |]
ballarin@20318
   558
        ==> h (x \<oplus>\<^bsub>G\<^esub> y) = h x \<oplus>\<^bsub>H\<^esub> h y"
ballarin@20318
   559
by (rule group_hom.hom_mult[OF a_group_hom,
ballarin@20318
   560
    simplified ring_record_simps])
ballarin@20318
   561
ballarin@20318
   562
lemma (in abelian_group_hom) hom_closed [simp]:
ballarin@20318
   563
  "x \<in> carrier G \<Longrightarrow> h x \<in> carrier H"
ballarin@20318
   564
by (rule group_hom.hom_closed[OF a_group_hom,
ballarin@20318
   565
    simplified ring_record_simps])
ballarin@20318
   566
ballarin@20318
   567
lemma (in abelian_group_hom) zero_closed [simp]:
ballarin@20318
   568
  "h \<zero> \<in> carrier H"
ballarin@20318
   569
by (rule group_hom.one_closed[OF a_group_hom,
ballarin@20318
   570
    simplified ring_record_simps])
ballarin@20318
   571
ballarin@20318
   572
lemma (in abelian_group_hom) hom_zero [simp]:
ballarin@20318
   573
  "h \<zero> = \<zero>\<^bsub>H\<^esub>"
ballarin@20318
   574
by (rule group_hom.hom_one[OF a_group_hom,
ballarin@20318
   575
    simplified ring_record_simps])
ballarin@20318
   576
ballarin@20318
   577
lemma (in abelian_group_hom) a_inv_closed [simp]:
ballarin@20318
   578
  "x \<in> carrier G ==> h (\<ominus>x) \<in> carrier H"
ballarin@20318
   579
by (rule group_hom.inv_closed[OF a_group_hom,
ballarin@20318
   580
    folded a_inv_def, simplified ring_record_simps])
ballarin@20318
   581
ballarin@20318
   582
lemma (in abelian_group_hom) hom_a_inv [simp]:
ballarin@20318
   583
  "x \<in> carrier G ==> h (\<ominus>x) = \<ominus>\<^bsub>H\<^esub> (h x)"
ballarin@20318
   584
by (rule group_hom.hom_inv[OF a_group_hom,
ballarin@20318
   585
    folded a_inv_def, simplified ring_record_simps])
ballarin@20318
   586
ballarin@20318
   587
lemma (in abelian_group_hom) additive_subgroup_a_kernel:
ballarin@20318
   588
  "additive_subgroup (a_kernel G H h) G"
ballarin@20318
   589
apply (rule additive_subgroup.intro)
ballarin@20318
   590
apply (rule group_hom.subgroup_kernel[OF a_group_hom,
ballarin@20318
   591
       folded a_kernel_def, simplified ring_record_simps])
ballarin@20318
   592
done
ballarin@20318
   593
ballarin@20318
   594
text{*The kernel of a homomorphism is an abelian subgroup*}
ballarin@20318
   595
lemma (in abelian_group_hom) abelian_subgroup_a_kernel:
ballarin@20318
   596
  "abelian_subgroup (a_kernel G H h) G"
ballarin@20318
   597
apply (rule abelian_subgroupI)
ballarin@20318
   598
apply (rule group_hom.normal_kernel[OF a_group_hom,
ballarin@20318
   599
       folded a_kernel_def, simplified ring_record_simps])
ballarin@20318
   600
apply (simp add: G.a_comm)
ballarin@20318
   601
done
ballarin@20318
   602
ballarin@20318
   603
lemma (in abelian_group_hom) A_FactGroup_nonempty:
ballarin@20318
   604
  assumes X: "X \<in> carrier (G A_Mod a_kernel G H h)"
ballarin@20318
   605
  shows "X \<noteq> {}"
ballarin@20318
   606
by (rule group_hom.FactGroup_nonempty[OF a_group_hom,
wenzelm@23350
   607
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps]) (rule X)
ballarin@20318
   608
ballarin@20318
   609
lemma (in abelian_group_hom) FactGroup_contents_mem:
ballarin@20318
   610
  assumes X: "X \<in> carrier (G A_Mod (a_kernel G H h))"
ballarin@20318
   611
  shows "contents (h`X) \<in> carrier H"
ballarin@20318
   612
by (rule group_hom.FactGroup_contents_mem[OF a_group_hom,
wenzelm@23350
   613
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps]) (rule X)
ballarin@20318
   614
ballarin@20318
   615
lemma (in abelian_group_hom) A_FactGroup_hom:
ballarin@20318
   616
     "(\<lambda>X. contents (h`X)) \<in> hom (G A_Mod (a_kernel G H h))
ballarin@20318
   617
          \<lparr>carrier = carrier H, mult = add H, one = zero H\<rparr>"
ballarin@20318
   618
by (rule group_hom.FactGroup_hom[OF a_group_hom,
ballarin@20318
   619
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps])
ballarin@20318
   620
ballarin@20318
   621
lemma (in abelian_group_hom) A_FactGroup_inj_on:
ballarin@20318
   622
     "inj_on (\<lambda>X. contents (h ` X)) (carrier (G A_Mod a_kernel G H h))"
ballarin@20318
   623
by (rule group_hom.FactGroup_inj_on[OF a_group_hom,
ballarin@20318
   624
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps])
ballarin@20318
   625
ballarin@20318
   626
text{*If the homomorphism @{term h} is onto @{term H}, then so is the
ballarin@20318
   627
homomorphism from the quotient group*}
ballarin@20318
   628
lemma (in abelian_group_hom) A_FactGroup_onto:
ballarin@20318
   629
  assumes h: "h ` carrier G = carrier H"
ballarin@20318
   630
  shows "(\<lambda>X. contents (h ` X)) ` carrier (G A_Mod a_kernel G H h) = carrier H"
ballarin@20318
   631
by (rule group_hom.FactGroup_onto[OF a_group_hom,
wenzelm@23350
   632
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps]) (rule h)
ballarin@20318
   633
ballarin@20318
   634
text{*If @{term h} is a homomorphism from @{term G} onto @{term H}, then the
ballarin@20318
   635
 quotient group @{term "G Mod (kernel G H h)"} is isomorphic to @{term H}.*}
ballarin@20318
   636
theorem (in abelian_group_hom) A_FactGroup_iso:
ballarin@20318
   637
  "h ` carrier G = carrier H
ballarin@20318
   638
   \<Longrightarrow> (\<lambda>X. contents (h`X)) \<in> (G A_Mod (a_kernel G H h)) \<cong>
ballarin@20318
   639
          (| carrier = carrier H, mult = add H, one = zero H |)"
ballarin@20318
   640
by (rule group_hom.FactGroup_iso[OF a_group_hom,
ballarin@20318
   641
    folded a_kernel_def A_FactGroup_def, simplified ring_record_simps])
ballarin@20318
   642
ballarin@20318
   643
section {* Lemmas Lifted from CosetExt.thy *}
ballarin@20318
   644
ballarin@20318
   645
text {* Not eveything from \texttt{CosetExt.thy} is lifted here. *}
ballarin@20318
   646
ballarin@20318
   647
subsection {* General Lemmas from \texttt{AlgebraExt.thy} *}
ballarin@20318
   648
ballarin@20318
   649
lemma (in additive_subgroup) a_Hcarr [simp]:
ballarin@20318
   650
  assumes hH: "h \<in> H"
ballarin@20318
   651
  shows "h \<in> carrier G"
ballarin@20318
   652
by (rule subgroup.mem_carrier [OF a_subgroup,
wenzelm@23350
   653
    simplified monoid_record_simps]) (rule hH)
ballarin@20318
   654
ballarin@20318
   655
ballarin@20318
   656
subsection {* Lemmas for Right Cosets *}
ballarin@20318
   657
ballarin@20318
   658
lemma (in abelian_subgroup) a_elemrcos_carrier:
ballarin@20318
   659
  assumes acarr: "a \<in> carrier G"
ballarin@20318
   660
      and a': "a' \<in> H +> a"
ballarin@20318
   661
  shows "a' \<in> carrier G"
ballarin@20318
   662
by (rule subgroup.elemrcos_carrier [OF a_subgroup a_group,
wenzelm@23350
   663
    folded a_r_coset_def, simplified monoid_record_simps]) (rule acarr, rule a')
ballarin@20318
   664
ballarin@20318
   665
lemma (in abelian_subgroup) a_rcos_const:
ballarin@20318
   666
  assumes hH: "h \<in> H"
ballarin@20318
   667
  shows "H +> h = H"
ballarin@20318
   668
by (rule subgroup.rcos_const [OF a_subgroup a_group,
wenzelm@23350
   669
    folded a_r_coset_def, simplified monoid_record_simps]) (rule hH)
ballarin@20318
   670
ballarin@20318
   671
lemma (in abelian_subgroup) a_rcos_module_imp:
ballarin@20318
   672
  assumes xcarr: "x \<in> carrier G"
ballarin@20318
   673
      and x'cos: "x' \<in> H +> x"
ballarin@20318
   674
  shows "(x' \<oplus> \<ominus>x) \<in> H"
ballarin@20318
   675
by (rule subgroup.rcos_module_imp [OF a_subgroup a_group,
wenzelm@23350
   676
    folded a_r_coset_def a_inv_def, simplified monoid_record_simps]) (rule xcarr, rule x'cos)
ballarin@20318
   677
ballarin@20318
   678
lemma (in abelian_subgroup) a_rcos_module_rev:
wenzelm@23350
   679
  assumes "x \<in> carrier G" "x' \<in> carrier G"
wenzelm@23350
   680
      and "(x' \<oplus> \<ominus>x) \<in> H"
ballarin@20318
   681
  shows "x' \<in> H +> x"
wenzelm@23350
   682
using assms
ballarin@20318
   683
by (rule subgroup.rcos_module_rev [OF a_subgroup a_group,
ballarin@20318
   684
    folded a_r_coset_def a_inv_def, simplified monoid_record_simps])
ballarin@20318
   685
ballarin@20318
   686
lemma (in abelian_subgroup) a_rcos_module:
wenzelm@23350
   687
  assumes "x \<in> carrier G" "x' \<in> carrier G"
ballarin@20318
   688
  shows "(x' \<in> H +> x) = (x' \<oplus> \<ominus>x \<in> H)"
wenzelm@23350
   689
using assms
ballarin@20318
   690
by (rule subgroup.rcos_module [OF a_subgroup a_group,
ballarin@20318
   691
    folded a_r_coset_def a_inv_def, simplified monoid_record_simps])
ballarin@20318
   692
ballarin@20318
   693
--"variant"
ballarin@20318
   694
lemma (in abelian_subgroup) a_rcos_module_minus:
ballarin@27611
   695
  assumes "ring G"
ballarin@20318
   696
  assumes carr: "x \<in> carrier G" "x' \<in> carrier G"
ballarin@20318
   697
  shows "(x' \<in> H +> x) = (x' \<ominus> x \<in> H)"
ballarin@20318
   698
proof -
ballarin@27611
   699
  interpret G: ring [G] by fact
ballarin@20318
   700
  from carr
wenzelm@23350
   701
  have "(x' \<in> H +> x) = (x' \<oplus> \<ominus>x \<in> H)" by (rule a_rcos_module)
wenzelm@23350
   702
  with carr
wenzelm@23350
   703
  show "(x' \<in> H +> x) = (x' \<ominus> x \<in> H)"
wenzelm@23350
   704
    by (simp add: minus_eq)
ballarin@20318
   705
qed
ballarin@20318
   706
ballarin@20318
   707
lemma (in abelian_subgroup) a_repr_independence':
wenzelm@23463
   708
  assumes y: "y \<in> H +> x"
wenzelm@23463
   709
      and xcarr: "x \<in> carrier G"
ballarin@20318
   710
  shows "H +> x = H +> y"
wenzelm@23463
   711
  apply (rule a_repr_independence)
wenzelm@23463
   712
    apply (rule y)
wenzelm@23463
   713
   apply (rule xcarr)
wenzelm@23463
   714
  apply (rule a_subgroup)
wenzelm@23463
   715
  done
ballarin@20318
   716
ballarin@20318
   717
lemma (in abelian_subgroup) a_repr_independenceD:
ballarin@20318
   718
  assumes ycarr: "y \<in> carrier G"
ballarin@20318
   719
      and repr:  "H +> x = H +> y"
ballarin@20318
   720
  shows "y \<in> H +> x"
ballarin@20318
   721
by (rule group.repr_independenceD [OF a_group a_subgroup,
wenzelm@23383
   722
    folded a_r_coset_def, simplified monoid_record_simps]) (rule ycarr, rule repr)
ballarin@20318
   723
ballarin@20318
   724
ballarin@20318
   725
subsection {* Lemmas for the Set of Right Cosets *}
ballarin@20318
   726
ballarin@20318
   727
lemma (in abelian_subgroup) a_rcosets_carrier:
ballarin@20318
   728
  "X \<in> a_rcosets H \<Longrightarrow> X \<subseteq> carrier G"
ballarin@20318
   729
by (rule subgroup.rcosets_carrier [OF a_subgroup a_group,
ballarin@20318
   730
    folded A_RCOSETS_def, simplified monoid_record_simps])
ballarin@20318
   731
ballarin@20318
   732
ballarin@20318
   733
ballarin@20318
   734
subsection {* Addition of Subgroups *}
ballarin@20318
   735
ballarin@20318
   736
lemma (in abelian_monoid) set_add_closed:
ballarin@20318
   737
  assumes Acarr: "A \<subseteq> carrier G"
ballarin@20318
   738
      and Bcarr: "B \<subseteq> carrier G"
ballarin@20318
   739
  shows "A <+> B \<subseteq> carrier G"
ballarin@20318
   740
by (rule monoid.set_mult_closed [OF a_monoid,
wenzelm@23383
   741
    folded set_add_def, simplified monoid_record_simps]) (rule Acarr, rule Bcarr)
ballarin@20318
   742
ballarin@20318
   743
lemma (in abelian_group) add_additive_subgroups:
ballarin@20318
   744
  assumes subH: "additive_subgroup H G"
ballarin@20318
   745
      and subK: "additive_subgroup K G"
ballarin@20318
   746
  shows "additive_subgroup (H <+> K) G"
ballarin@20318
   747
apply (rule additive_subgroup.intro)
ballarin@20318
   748
apply (unfold set_add_def)
ballarin@20318
   749
apply (intro comm_group.mult_subgroups)
ballarin@20318
   750
  apply (rule a_comm_group)
ballarin@20318
   751
 apply (rule additive_subgroup.a_subgroup[OF subH])
ballarin@20318
   752
apply (rule additive_subgroup.a_subgroup[OF subK])
ballarin@20318
   753
done
ballarin@20318
   754
ballarin@20318
   755
end