Theory TopologicalGroup_ZF

theory TopologicalGroup_ZF
imports Topology_ZF_3 Group_ZF_1 Semigroup_ZF
(* 
This file is a part of IsarMathLib -
a library of formalized mathematics written for Isabelle/Isar.

Copyright (C) 2009-2013 Slawomir Kolodynski

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*)


header{*\isaheader{TopologicalGroup\_ZF.thy}*}

theory TopologicalGroup_ZF imports Topology_ZF_3 Group_ZF_1 Semigroup_ZF

begin

text{*This theory is about the first subject of algebraic topology:
topological groups.*}


section{*Topological group: definition and notation*}

text{*Topological group is a group that is a topological space
at the same time. This means that a topological group is a triple of sets,
say $(G,f,T)$ such that $T$ is a topology on $G$, $f$ is a group
operation on $G$ and both $f$ and the operation of taking inverse in $G$
are continuous. Since IsarMathLib defines topology without using the carrier,
(see @{text "Topology_ZF"}), in our setup we just use $\bigcup T$ instead
of $G$ and say that the pair of sets $(\bigcup T , f)$ is a group.
This way our definition of being a topological group is a statement about two
sets: the topology $T$ and the group operation $f$ on $G=\bigcup T$.
Since the domain of the group operation is $G\times G$, the pair of
topologies in which $f$ is supposed to be continuous is $T$ and
the product topology on $G\times G$ (which we will call $\tau$ below).*}


text{*This way we arrive at the following definition of a predicate that
states that pair of sets is a topological group.*}


definition
"IsAtopologicalGroup(T,f) ≡ (T {is a topology}) ∧ IsAgroup(\<Union>T,f) ∧
IsContinuous(ProductTopology(T,T),T,f) ∧
IsContinuous(T,T,GroupInv(\<Union>T,f))"


text{*We will inherit notation from the @{text "topology0"} locale. That locale assumes that
$T$ is a topology. For convenience we will denote $G=\bigcup T$ and $\tau$ to be
the product topology on $G\times G$. To that we add some
notation specific to groups. We will use additive notation
for the group operation, even though we don't assume that the group is abelian.
The notation $g+A$ will mean the left translation of the set $A$ by element $g$, i.e.
$g+A=\{g+a|a\in A\}$.
The group operation $G$ induces a natural operation on the subsets of $G$
defined as $\langle A,B\rangle \mapsto \{x+y | x\in A, y\in B \}$.
Such operation has been considered in @{text "func_ZF"} and called
$f$ ''lifted to subsets of'' $G$. We will denote the value of such operation
on sets $A,B$ as $A+B$.
The set of neigboorhoods of zero (denoted @{text "\<N>0"}) is the
collection of (not necessarily open) sets whose interior contains the neutral
element of the group.*}


locale topgroup = topology0 +

fixes G
defines G_def [simp]: "G ≡ \<Union>T"

fixes prodtop ("τ")
defines prodtop_def [simp]: "τ ≡ ProductTopology(T,T)"

fixes f

assumes Ggroup: "IsAgroup(G,f)"

assumes fcon: "IsContinuous(τ,T,f)"

assumes inv_cont: "IsContinuous(T,T,GroupInv(G,f))"

fixes grop (infixl "\<ra>" 90)
defines grop_def [simp]: "x\<ra>y ≡ f`⟨x,y⟩"

fixes grinv ("\<rm> _" 89)
defines grinv_def [simp]: "(\<rm>x) ≡ GroupInv(G,f)`(x)"

fixes grsub (infixl "\<rs>" 90)
defines grsub_def [simp]: "x\<rs>y ≡ x\<ra>(\<rm>y)"

fixes setinv ("\<sm> _" 72)
defines setninv_def [simp]: "\<sm>A ≡ GroupInv(G,f)``(A)"

fixes ltrans (infix "\<ltr>" 73)
defines ltrans_def [simp]: "x \<ltr> A ≡ LeftTranslation(G,f,x)``(A)"

fixes rtrans (infix "\<rtr>" 73)
defines rtrans_def [simp]: "A \<rtr> x ≡ RightTranslation(G,f,x)``(A)"

fixes setadd (infixl "\<sad>" 71)
defines setadd_def [simp]: "A\<sad>B ≡ (f {lifted to subsets of} G)`⟨A,B⟩"

fixes gzero ("\<zero>")
defines gzero_def [simp]: "\<zero> ≡ TheNeutralElement(G,f)"

fixes zerohoods ("\<N>0")
defines zerohoods_def [simp]: "\<N>0 ≡ {A ∈ Pow(G). \<zero> ∈ int(A)}"

fixes listsum ("∑ _" 70)
defines listsum_def[simp]: "∑k ≡ Fold1(f,k)"

text{*The first lemma states that we indeeed talk about topological group
in the context of @{text "topgroup"} locale.*}


lemma (in topgroup) topGroup: shows "IsAtopologicalGroup(T,f)"
using topSpaceAssum Ggroup fcon inv_cont IsAtopologicalGroup_def
by simp;

text{* If a pair of sets $(T,f)$ forms a topological group, then
all theorems proven in the @{text "topgroup"} context are valid as applied to
$(T,f)$.*}


lemma topGroupLocale: assumes "IsAtopologicalGroup(T,f)"
shows "topgroup(T,f)"
using assms IsAtopologicalGroup_def topgroup_def
topgroup_axioms.intro topology0_def by simp;

text{*We can use the @{text "group0"} locale in the context of @{text "topgroup"}.*}

lemma (in topgroup) group0_valid_in_tgroup: shows "group0(G,f)"
using Ggroup group0_def by simp

text{*We can use @{text "semigr0"} locale in the context of @{text "topgroup"}. *}

lemma (in topgroup) semigr0_valid_in_tgroup: shows "semigr0(G,f)"
using Ggroup IsAgroup_def IsAmonoid_def semigr0_def by simp

text{*We can use the @{text "prod_top_spaces0"} locale in the context of @{text "topgroup"}.*}

lemma (in topgroup) prod_top_spaces0_valid: shows "prod_top_spaces0(T,T,T)"
using topSpaceAssum prod_top_spaces0_def by simp

text{*Negative of a group element is in group.*}

lemma (in topgroup) neg_in_tgroup: assumes "g∈G" shows "(\<rm>g) ∈ G"
proof -
from assms have "GroupInv(G,f)`(g) ∈ G"
using group0_valid_in_tgroup group0.inverse_in_group by blast
thus ?thesis by simp
qed

text{*Zero is in the group.*}

lemma (in topgroup) zero_in_tgroup: shows "\<zero>∈G"
proof -
have "TheNeutralElement(G,f) ∈ G"
using group0_valid_in_tgroup group0.group0_2_L2 by blast
then show "\<zero>∈G" by simp
qed

text{*Of course the product topology is a topology (on $G\times G$).*}

lemma (in topgroup) prod_top_on_G:
shows "τ {is a topology}" and "\<Union>τ = G×G"
using topSpaceAssum Top_1_4_T1 by auto;

text{*Let's recall that $f$ is a binary operation on $G$ in this context.*}

lemma (in topgroup) topgroup_f_binop: shows "f : G×G -> G"
using Ggroup group0_def group0.group_oper_assocA by simp;

text{*A subgroup of a topological group is a topological group
with relative topology
and restricted operation. Relative topology is the same
as @{text "T {restricted to} H"}
which is defined to be $\{V \cap H: V\in T\}$ in @{text "ZF1"} theory.*}


lemma (in topgroup) top_subgroup: assumes A1: "IsAsubgroup(H,f)"
shows "IsAtopologicalGroup(T {restricted to} H,restrict(f,H×H))"
proof -
let 0 = "T {restricted to} H"
let ?fH = "restrict(f,H×H)"
have "\<Union>?τ0 = G ∩ H" using union_restrict by simp;
also from A1 have "… = H"
using group0_valid_in_tgroup group0.group0_3_L2 by blast;
finally have "\<Union>?τ0 = H" by simp;
have "?τ0 {is a topology}" using Top_1_L4 by simp;
moreover from A1 `\<Union>?τ0 = H` have "IsAgroup(\<Union>?τ0,?fH)"
using IsAsubgroup_def by simp;
moreover have "IsContinuous(ProductTopology(?τ0,?τ0),?τ0,?fH)"
proof -
have "two_top_spaces0(τ, T,f)"
using topSpaceAssum prod_top_on_G topgroup_f_binop prod_top_on_G
two_top_spaces0_def by simp;
moreover
from A1 have "H ⊆ G" using group0_valid_in_tgroup group0.group0_3_L2
by simp;
then have "H×H ⊆ \<Union>τ" using prod_top_on_G by auto;
moreover have "IsContinuous(τ,T,f)" using fcon by simp;
ultimately have
"IsContinuous(τ {restricted to} H×H, T {restricted to} ?fH``(H×H),?fH)"
using two_top_spaces0.restr_restr_image_cont by simp;
moreover have
"ProductTopology(?τ0,?τ0) = τ {restricted to} H×H"
using topSpaceAssum prod_top_restr_comm by simp;
moreover from A1 have "?fH``(H×H) = H" using image_subgr_op
by simp;
ultimately show ?thesis by simp;
qed
moreover have "IsContinuous(?τ0,?τ0,GroupInv(\<Union>?τ0,?fH))"
proof -
let ?g = "restrict(GroupInv(G,f),H)"
have "GroupInv(G,f) : G -> G"
using Ggroup group0_2_T2 by simp;
then have "two_top_spaces0(T,T,GroupInv(G,f))"
using topSpaceAssum two_top_spaces0_def by simp;
moreover from A1 have "H ⊆ \<Union>T"
using group0_valid_in_tgroup group0.group0_3_L2
by simp;
ultimately have
"IsContinuous(?τ0,T {restricted to} ?g``(H),?g)"
using inv_cont two_top_spaces0.restr_restr_image_cont
by simp;
moreover from A1 have "?g``(H) = H"
using group0_valid_in_tgroup group0.restr_inv_onto
by simp;
moreover
from A1 have "GroupInv(H,?fH) = ?g"
using group0_valid_in_tgroup group0.group0_3_T1
by simp;
with `\<Union>?τ0 = H` have "?g = GroupInv(\<Union>?τ0,?fH)" by simp;
ultimately show ?thesis by simp;
qed
ultimately show ?thesis unfolding IsAtopologicalGroup_def by simp;
qed

section{*Interval arithmetic, translations and inverse of set*}

text{*In this section we list some properties of operations of translating a
set and reflecting it around the neutral element of the group. Many of the results
are proven in other theories, here we just collect them and rewrite in notation
specific to the @{text "topgroup"} context.*}


text{*Different ways of looking at adding sets.*}

lemma (in topgroup) interval_add: assumes "A⊆G" "B⊆G" shows
"A\<sad>B ⊆ G" and "A\<sad>B = f``(A×B)" "A\<sad>B = (\<Union>x∈A. x\<ltr>B)"
proof -
from assms show "A\<sad>B ⊆ G" and "A\<sad>B = f``(A×B)"
using topgroup_f_binop lift_subsets_explained by auto
from assms show "A\<sad>B = (\<Union>x∈A. x\<ltr>B)"
using group0_valid_in_tgroup group0.image_ltrans_union by simp
qed

text{*Right and left translations are continuous.*}

lemma (in topgroup) trans_cont: assumes "g∈G" shows
"IsContinuous(T,T,RightTranslation(G,f,g))" and
"IsContinuous(T,T,LeftTranslation(G,f,g))"
using assms group0_valid_in_tgroup group0.trans_eq_section
topgroup_f_binop fcon prod_top_spaces0_valid
prod_top_spaces0.fix_1st_var_cont prod_top_spaces0.fix_2nd_var_cont
by auto

text{*Left and right translations of an open set are open.*}

lemma (in topgroup) open_tr_open: assumes "g∈G" and "V∈T"
shows "g\<ltr>V ∈ T" and "V\<rtr>g ∈ T"
using assms neg_in_tgroup trans_cont IsContinuous_def
group0_valid_in_tgroup group0.trans_image_vimage by auto

text{*Right and left translations are homeomorphisms.*}

lemma (in topgroup) tr_homeo: assumes "g∈G" shows
"IsAhomeomorphism(T,T,RightTranslation(G,f,g))" and
"IsAhomeomorphism(T,T,LeftTranslation(G,f,g))"
using assms group0_valid_in_tgroup group0.trans_bij trans_cont open_tr_open
bij_cont_open_homeo by auto

text{*Translations preserve interior.*}

lemma (in topgroup) trans_interior: assumes A1: "g∈G" and A2: "A⊆G"
shows "g \<ltr> int(A) = int(g\<ltr>A)"
proof -
from assms have "A ⊆ \<Union>T" and "IsAhomeomorphism(T,T,LeftTranslation(G,f,g))"
using tr_homeo by auto
then show ?thesis using int_top_invariant by simp
qed
(*
text{*Translating by an inverse and then by an element cancels out.*}

lemma (in topgroup) trans_inverse_elem: assumes "g∈G" and "A⊆G"
shows "g\<ltr>((\<rm>g)\<ltr>A) = A"
using assms neg_in_tgroup group0_valid_in_tgroup group0.trans_comp_image
group0.group0_2_L6 group0.trans_neutral image_id_same by simp*)


text{*Inverse of an open set is open.*}

lemma (in topgroup) open_inv_open: assumes "V∈T" shows "(\<sm>V) ∈ T"
using assms group0_valid_in_tgroup group0.inv_image_vimage
inv_cont IsContinuous_def by simp

text{*Inverse is a homeomorphism.*}

lemma (in topgroup) inv_homeo: shows "IsAhomeomorphism(T,T,GroupInv(G,f))"
using group0_valid_in_tgroup group0.group_inv_bij inv_cont open_inv_open
bij_cont_open_homeo by simp

text{*Taking negative preserves interior.*}

lemma (in topgroup) int_inv_inv_int: assumes "A ⊆ G"
shows "int(\<sm>A) = \<sm>(int(A))"
using assms inv_homeo int_top_invariant by simp

section{*Neighborhoods of zero*}

text{*Zero neighborhoods are (not necessarily open) sets whose interior
contains the neutral element of the group. In the @{text "topgroup"} locale
the collection of neighboorhoods of zero is denoted @{text "\<N>0"}. *}


text{*The whole space is a neighborhood of zero.*}

lemma (in topgroup) zneigh_not_empty: shows "G ∈ \<N>0"
using topSpaceAssum IsATopology_def Top_2_L3 zero_in_tgroup
by simp

text{*Any element belongs to the interior of any neighboorhood of zero
translated by that element.*}


lemma (in topgroup) elem_in_int_trans:
assumes A1: "g∈G" and A2: "H ∈ \<N>0"
shows "g ∈ int(g\<ltr>H)"
proof -
from A2 have "\<zero> ∈ int(H)" and "int(H) ⊆ G" using Top_2_L2 by auto
with A1 have "g ∈ g \<ltr> int(H)"
using group0_valid_in_tgroup group0.neut_trans_elem by simp
with assms show ?thesis using trans_interior by simp
qed

text{*Negative of a neighborhood of zero is a neighborhood of zero.*}

lemma (in topgroup) neg_neigh_neigh: assumes "H ∈ \<N>0"
shows "(\<sm>H) ∈ \<N>0"
proof -
from assms have "int(H) ⊆ G" and "\<zero> ∈ int(H)" using Top_2_L1 by auto
with assms have "\<zero> ∈ int(\<sm>H)" using group0_valid_in_tgroup group0.neut_inv_neut
int_inv_inv_int by simp
moreover
have "GroupInv(G,f):G->G" using Ggroup group0_2_T2 by simp
then have "(\<sm>H) ⊆ G" using func1_1_L6 by simp
ultimately show ?thesis by simp
qed

text{*Translating an open set by a negative of a point that belongs to it
makes it a neighboorhood of zero.*}


lemma (in topgroup) open_trans_neigh: assumes A1: "U∈T" and "g∈U"
shows "(\<rm>g)\<ltr>U ∈ \<N>0"
proof -
let ?H = "(\<rm>g)\<ltr>U"
from assms have "g∈G" by auto
then have "(\<rm>g) ∈ G" using neg_in_tgroup by simp
with A1 have "?H∈T" using open_tr_open by simp
hence "?H ⊆ G" by auto
moreover have "\<zero> ∈ int(?H)"
proof -
from assms have "U⊆G" and "g∈U" by auto
with `?H∈T` show "\<zero> ∈ int(?H)"
using group0_valid_in_tgroup group0.elem_trans_neut Top_2_L3
by auto
qed
ultimately show ?thesis by simp
qed

section{*Closure in topological groups*}

text{*This section is devoted to a characterization of closure
in topological groups.*}


text{*Closure of a set is contained in the sum of the set and any
neighboorhood of zero.*}


lemma (in topgroup) cl_contains_zneigh:
assumes A1: "A⊆G" and A2: "H ∈ \<N>0"
shows "cl(A) ⊆ A\<sad>H"
proof
fix x assume "x ∈ cl(A)"
from A1 have "cl(A) ⊆ G" using Top_3_L11 by simp
with `x ∈ cl(A)` have "x∈G" by auto
have "int(H) ⊆ G" using Top_2_L2 by auto
let ?V = "int(x \<ltr> (\<sm>H))"
have "?V = x \<ltr> (\<sm>int(H))"
proof -
from A2 `x∈G` have "?V = x \<ltr> int(\<sm>H)"
using neg_neigh_neigh trans_interior by simp
with A2 show ?thesis using int_inv_inv_int by simp
qed
have "A∩?V ≠ 0"
proof -
from A2 `x∈G` `x ∈ cl(A)` have "?V∈T" and "x ∈ cl(A) ∩ ?V"
using neg_neigh_neigh elem_in_int_trans Top_2_L2 by auto
with A1 show "A∩?V ≠ 0" using cl_inter_neigh by simp
qed
then obtain y where "y∈A" and "y∈?V" by auto
with `?V = x \<ltr> (\<sm>int(H))` `int(H) ⊆ G` `x∈G` have "x ∈ y\<ltr>int(H)"
using group0_valid_in_tgroup group0.ltrans_inv_in by simp
with `y∈A` have "x ∈ (\<Union>y∈A. y\<ltr>H)" using Top_2_L1 func1_1_L8 by auto
with assms show "x ∈ A\<sad>H" using interval_add by simp
qed

text{*The next theorem provides a characterization of closure in topological
groups in terms of neighborhoods of zero.*}


theorem (in topgroup) cl_topgroup:
assumes "A⊆G" shows "cl(A) = (\<Inter>H∈\<N>0. A\<sad>H)"
proof
from assms show "cl(A) ⊆ (\<Inter>H∈\<N>0. A\<sad>H)"
using zneigh_not_empty cl_contains_zneigh by auto
next
{ fix x assume "x ∈ (\<Inter>H∈\<N>0. A\<sad>H)"
then have "x ∈ A\<sad>G" using zneigh_not_empty by auto
with assms have "x∈G" using interval_add by blast
have "∀U∈T. x∈U --> U∩A ≠ 0"
proof -
{ fix U assume "U∈T" and "x∈U"
let ?H = "\<sm>((\<rm>x)\<ltr>U)"
from `U∈T` and `x∈U` have "(\<rm>x)\<ltr>U ⊆ G" and "?H ∈ \<N>0"
using open_trans_neigh neg_neigh_neigh by auto
with `x ∈ (\<Inter>H∈\<N>0. A\<sad>H)` have "x ∈ A\<sad>?H" by auto
with assms `?H ∈ \<N>0` obtain y where "y∈A" and "x ∈ y\<ltr>?H"
using interval_add by auto
have "y∈U"
proof -
from assms `y∈A` have "y∈G" by auto
with `(\<rm>x)\<ltr>U ⊆ G` and `x ∈ y\<ltr>?H` have "y ∈ x\<ltr>((\<rm>x)\<ltr>U)"
using group0_valid_in_tgroup group0.ltrans_inv_in by simp
with `U∈T` `x∈G` show "y∈U"
using neg_in_tgroup group0_valid_in_tgroup group0.trans_comp_image
group0.group0_2_L6 group0.trans_neutral image_id_same
by auto
qed
with `y∈A` have "U∩A ≠ 0" by auto
} thus ?thesis by simp
qed
with assms `x∈G` have "x ∈ cl(A)" using inter_neigh_cl by simp
} thus "(\<Inter>H∈\<N>0. A\<sad>H) ⊆ cl(A)" by auto
qed

section{*Sums of sequences of elements and subsets*}

text{* In this section we consider properties of the function $G^n\rightarrow G$,
$x=(x_0,x_1,...,x_{n-1})\mapsto \sum_{i=0}^{n-1}x_i$. We will model the cartesian product
$G^n$ by the space of sequences $n\rightarrow G$, where $n=\{0,1,...,n-1]\}$ is a natural number.
This space is equipped with a natural product topology defined in @{text "Topology_ZF_3"}. *}


text{*Let's recall first that the sum of elements of a group is an element of the group.*}

lemma (in topgroup) sum_list_in_group:
assumes "n ∈ nat" and "x: succ(n)->G"
shows "(∑x) ∈ G"
proof -
from assms have "semigr0(G,f)" and "n ∈ nat" "x: succ(n)->G"
using semigr0_valid_in_tgroup by auto
then have "Fold1(f,x) ∈ G" by (rule semigr0.prod_type)
thus "(∑x) ∈ G" by simp
qed

text{*In this context @{text"x\<ra>y"} is the same as the value of the group operation
on the elements $x$ and $y$. Normally we shouldn't need to state this a s separate lemma.
*}


lemma (in topgroup) grop_def1: shows "f`⟨x,y⟩ = x\<ra>y" by simp

text{*Another theorem from @{text "Semigroup_ZF"} theory that is useful to have in the
additive notation. *}


lemma (in topgroup) shorter_set_add:
assumes "n ∈ nat" and "x: succ(succ(n))->G"
shows "(∑x) = (∑Init(x)) \<ra> (x`(succ(n)))"
proof -
from assms have "semigr0(G,f)" and "n ∈ nat" "x: succ(succ(n))->G"
using semigr0_valid_in_tgroup by auto
then have "Fold1(f,x) = f`⟨Fold1(f,Init(x)),x`(succ(n))⟩"
by (rule semigr0.shorter_seq)
thus ?thesis by simp
qed

text{*Sum is a continuous function in the product topology.*}

theorem (in topgroup) sum_continuous: assumes "n ∈ nat"
shows "IsContinuous(SeqProductTopology(succ(n),T),T,{⟨x,∑x⟩.x∈succ(n)->G})"
proof -
note `n ∈ nat`
moreover have "IsContinuous(SeqProductTopology(succ(0),T),T,{⟨x,∑x⟩.x∈succ(0)->G})"
proof -
have "{⟨x,∑x⟩.x∈succ(0)->G} = {⟨x,x`(0)⟩. x∈1->G}"
using semigr0_valid_in_tgroup semigr0.prod_of_1elem by simp
moreover have
"IsAhomeomorphism(SeqProductTopology(1,T),T,{⟨x,x`(0)⟩. x∈1->\<Union>T})"
using topSpaceAssum singleton_prod_top1 by simp
ultimately show ?thesis using IsAhomeomorphism_def by simp
qed
moreover have "∀k∈nat.
IsContinuous(SeqProductTopology(succ(k),T),T,{⟨x,∑x⟩.x∈succ(k)->G})
-->
IsContinuous(SeqProductTopology(succ(succ(k)),T),T,{⟨x,∑x⟩.x∈succ(succ(k))->G})"

proof -
{ fix k assume "k ∈ nat"
let ?s = "{⟨x,∑x⟩.x∈succ(k)->G}"
let ?g = "{⟨p,⟨?s`(fst(p)),snd(p)⟩⟩. p ∈ (succ(k)->G)×G}"
let ?h = "{⟨x,⟨Init(x),x`(succ(k))⟩⟩. x ∈ succ(succ(k))->G}"
let = "SeqProductTopology(succ(k),T)"
let = "SeqProductTopology(succ(succ(k)),T)"
assume "IsContinuous(?φ,T,?s)"
from `k ∈ nat` have "?s: (succ(k)->G) -> G"
using sum_list_in_group ZF_fun_from_total by simp
have "?h: (succ(succ(k))->G)->(succ(k)->G)×G"
proof -
{ fix x assume "x ∈ succ(succ(k))->G"
with `k ∈ nat` have "Init(x) ∈ (succ(k)->G)"
using init_props by simp
with `k ∈ nat` `x : succ(succ(k))->G`
have "⟨Init(x),x`(succ(k))⟩ ∈ (succ(k)->G)×G"
using apply_funtype by blast
} then show ?thesis using ZF_fun_from_total by simp
qed
moreover have "?g:((succ(k)->G)×G)->(G×G)"
proof -
{ fix p assume "p ∈ (succ(k)->G)×G"
hence "fst(p): succ(k)->G" and "snd(p) ∈ G" by auto
with `?s: (succ(k)->G) -> G` have "⟨?s`(fst(p)),snd(p)⟩ ∈ G×G"
using apply_funtype by blast
} then show "?g:((succ(k)->G)×G)->(G×G)" using ZF_fun_from_total
by simp
qed
moreover have "f : G×G -> G" using topgroup_f_binop by simp
ultimately have "f O ?g O ?h :(succ(succ(k))->G)->G" using comp_fun
by blast
from `k ∈ nat` have "IsContinuous(?ψ,ProductTopology(?φ,T),?h)"
using topSpaceAssum finite_top_prod_homeo IsAhomeomorphism_def
by simp
moreover have "IsContinuous(ProductTopology(?φ,T),τ,?g)"
proof -
from topSpaceAssum have
"T {is a topology}" "?φ {is a topology}" "\<Union>?φ = succ(k)->G"
using seq_prod_top_is_top by auto
moreover from `\<Union>?φ = succ(k)->G` `?s: (succ(k)->G) -> G`
have "?s:\<Union>?φ->\<Union>T" by simp
moreover note `IsContinuous(?φ,T,?s)`
moreover from `\<Union>?φ = succ(k)->G`
have "?g = {⟨p,⟨?s`(fst(p)),snd(p)⟩⟩. p ∈ \<Union>?φ×\<Union>T}"
by simp
ultimately have "IsContinuous(ProductTopology(?φ,T),ProductTopology(T,T),?g)"
using cart_prod_cont1 by blast
thus ?thesis by simp
qed
moreover have "IsContinuous(τ,T,f)" using fcon by simp
moreover have "{⟨x,∑x⟩.x∈succ(succ(k))->G} = f O ?g O ?h"
proof -
let ?d = "{⟨x,∑x⟩.x∈succ(succ(k))->G}"
from `k∈nat` have "∀x∈succ(succ(k))->G. (∑x) ∈ G"
using sum_list_in_group by blast
then have "?d:(succ(succ(k))->G)->G"
using sum_list_in_group ZF_fun_from_total by simp
moreover note `f O ?g O ?h :(succ(succ(k))->G)->G`
moreover have "∀x∈succ(succ(k))->G. ?d`(x) = (f O ?g O ?h)`(x)"
proof
fix x assume "x∈succ(succ(k))->G"
then have I: "?h`(x) = ⟨Init(x),x`(succ(k))⟩"
using ZF_fun_from_tot_val1 by simp
moreover from `k∈nat` `x∈succ(succ(k))->G`
have "Init(x): succ(k)->G"
using init_props by simp
moreover from `k∈nat` `x:succ(succ(k))->G`
have II: "x`(succ(k)) ∈ G"
using apply_funtype by blast
ultimately have "?h`(x) ∈ (succ(k)->G)×G" by simp
then have "?g`(?h`(x)) = ⟨?s`(fst(?h`(x))),snd(?h`(x))⟩"
using ZF_fun_from_tot_val1 by simp
with I have "?g`(?h`(x)) = ⟨?s`(Init(x)),x`(succ(k))⟩"
by simp
with `Init(x): succ(k)->G` have "?g`(?h`(x)) = ⟨∑Init(x),x`(succ(k))⟩"
using ZF_fun_from_tot_val1 by simp
with `k ∈ nat` `x: succ(succ(k))->G`
have "f`(?g`(?h`(x))) = (∑x)"
using shorter_set_add by simp
with `x ∈ succ(succ(k))->G` have "f`(?g`(?h`(x))) = ?d`(x)"
using ZF_fun_from_tot_val1 by simp
moreover from
`?h: (succ(succ(k))->G)->(succ(k)->G)×G`
`?g:((succ(k)->G)×G)->(G×G)`
`f:(G×G)->G` `x∈succ(succ(k))->G`
have "(f O ?g O ?h)`(x) = f`(?g`(?h`(x)))" by (rule func1_1_L18)
ultimately show "?d`(x) = (f O ?g O ?h)`(x)" by simp
qed
ultimately show "{⟨x,∑x⟩.x∈succ(succ(k))->G} = f O ?g O ?h"
using func_eq by simp
qed
moreover note `IsContinuous(τ,T,f)`
ultimately have "IsContinuous(?ψ,T,{⟨x,∑x⟩.x∈succ(succ(k))->G})"
using comp_cont3 by simp
} thus ?thesis by simp
qed
ultimately show ?thesis by (rule ind_on_nat)
qed
end