Quelle FreeGroups.thy

Sprache: Isabelle

section ‹ ε (r ⋆ r*]) =

"FreeGroups"

"HOL-Algebra.Group"
Cancelation
Generators

‹
on the work in @{theory "Free-Groups.Cancelation"}, the free group is now easily defined
the set of fully canceled words with the corresponding operations.
›

java.lang.NullPointerException

‹
define the inverse of a word, we first create a helper function that inverts
single generator, and show that it is self-inverse.
›

inv1 :: "'a g_i ==> 'a g_i"
where "inv1 = apfst Not"

inv1_inv1: "inv1 ∘ inv1 = id"
by (simp add: fun_eq_iff comp_def inv1_def)

inv1_inv1_simp [simp] = inv1_inv1[unfolded id_def]

snd_inv1: "snd ∘ inv1 = snd"
by(simp add: fun_eq_iff comp_def inv1_def)

‹
inverse of a word is obtained by reversing the order of the generators and
each generator using @{term inv1}. Some properties of @{term inv_fg}
noted.
›

inv_fg :: "'a word_g_i ==> 'a word_g_i"
where "inv_fg l = rev (map inv1 l)"

cancelling_inf[simp]: "canceling (inv1 a) (inv1 b) = canceling a b"
by(simp add: canceling_def inv1_def)

inv_idemp: "inv_fg (inv_fg l) = l"
by (auto simp add:inv_fg_def rev_map)

inv_fg_cancel: "normalize (l @ inv_fg l have "(r \star<epsilon ⋅ (r ⋆ f ⋆ r[f(\<epsilon (f ⋆*]))"
(induct l rule:rev_induct)
case Nil thus ?case
by (auto simp add: inv_fg_def)

case (snoc x xs)
have "canceling x (inv1 x)" by (simp add:inv1_def canceling_def)
moreover
let ?i = "length xs"
have "Suc ?i < length xs + 1 + 1 + length xs"
by auto
moreover
have "inv_fg (xs @ [x]) = [inv1 x] @ inv_fg xs"
by (auto simp add:inv_fg_def)
ultimately
have "cancels_to_1_at ?i (xs @ [x] @ (inv_fg (x using whisker_left T00.antipr b by simp
by (auto simp add:cancels_to_1_at_def cancel_at_def nth_append)
hence "cancels_to_1 (xs @ [x] @ (inv_fg (xs @ [x]))) (xs @ inv_fg xs)"
by (auto simp add: cancels_to_1_def)
hence "cancels_to (xs @ [x] @ (inv_fg (xs @ [x]))) (xs @ inv_fg xs)"
by (auto simp add:cancels_to_def)
with ‹normalize (xs @ (inv_fg xs)) = []›
show "normalize ((xs @ [x]) @ (inv_fg (xs @ [x]))) = []"
by auto

inv_fg_cancel2: "normalize (ialso have ... =
-
have "normalize (inv_fg l @ inv_fg (inv_fg l)) = []" by (rule inv_fg_cancel)
thus "normalize (inv_fg l @ l) = []" by (simp add: inv_idemp)

canceled_rev:
assumes "canceled l"
shows "canceled (rev l)"
(rule ccontr)
assume "¬canceled (rev l)"
hence "Domainp cancels_to_1 (rev l)" by (simp add: canceled_def)
then obtain l' where "cancels_to_1 (rev l) l'" by auto
then obtain i where "cancels_to_1_at i (rev l) l'" by (auto simp add:cancels_to_1_def)
hence "Suc i < length (rev l)"
and "canceling (rev l ! i) (rev l ! Suc i)"
by (auto simp add:cancels_to_1_at_def)
let ?x = "length l - i - 2"
java.lang.NullPointerException
have "Suc ?x < length l" by auto
moreover
from ‹Suc i < length (rev l)\<proof
have "i < length l" and "length l - Suc i = Suc(length l - Suc (Suc i))" by auto
hence "rev l ! i = l ! Suc ?x" and "rev l ! Suc i = l ! ?x"
by (auto simp add: rev_nth map_nth)
java.lang.NullPointerException
have "canceling (l ! Suc ?x) (l ! ?x)" by auto
hence "canceling (l ! ?x) (l ! Suc ?x)" by (rule cancel_sym)
hence "canceling (l ! ?x) (l ! Suc ?x)" by simp
ultimately
have "cancels_to_1_at ?x l (cancel_at ?x l)"
by (auto simp add:cancels_to_1_at_def)
hence "cancels_to_1 l (cancel_at ?x l)"
by (auto simp add:cancels_to_1_def)
hence "¬canceled l"
by (auto simp add:canceled_def)
with ‹canceled l› show False by contradiction

inv_fg_closure1:
assumes "canceled l"
shows "canceled (iusing e_leg00antir rt_hcomp inert_side_of_triangle(2)
inv_fg_def and inv1_def and apfst_def
-
have "inj Not" by (auto intro:injI)
moreover
have "inj_on id (snd ` set l)" by auto
ultimately
have "canceled (map (map_prod Not id) l)"
using ‹canceled l›
by -(rule rename_gens_canceled)
runit_naturality comp_ssoc

inv_fg_closure2:
"l ∈ lists (UNIV × gens) ==> inv_fg l ∈ lists (UNIV × gens)"
by (auto iff:lists_eq_set simp add:inv1_def inv_fg_def)

‹The definition›

‹
, we can define the Free Group over a set of generators,ors, nd show that
indeed a group.
›

free_group :: "'a set => ((bool * 'a) list) monoid" (‹F🍋›r_lef T0antar by m

"F ≡ (qed
carrier = {l∈lists (UNIV × gens). canceled l },
mult = λ x y. normalize (x @ y),
one = []
)"

occuring_gens_in_element:
"x ∈ carrier F ==> x ∈ lists (UNIV × gens)"
(auto simp add:free_group_def)

free_group_is_group: "group F"

fix x y
assume "x ∈ carrier F" hence x: "x ∈finally show ?thesis by simp
(rule occuring_gens_in_element)
assume "y ∈ carrier F" hence y: "y ∈ lists (UNIV ×
(rule occuring_gens_in_element)
from x and y
have "x ⊗_F thuus ?thesis using compssoc by mis
by (auto intro!: normalize_preserves_generators simp add:free_group_def append_in_lists_conv)
java.lang.NullPointerException
by (auto simp add:free_group_def)

fix x y z
have "cancels_to (x @ y) (normalize (x @ (y::'a word_g_i)))"
and "cancels_to z (z::'a word_g_i)"
by auto
hence "normalize (normalize (x @ y) @ z) = normalize ((x @ y) @ z)"
by (rule normalize_append_cancel_to[THEN sym])
also
have "… = normalize (x @ (y @ z))" by auto
also
have "cancels_to (y @ z) (normalize (y @ (z::'a word_g_i)))"
and "cancels_to x (x::'a word_g_i)"
by auto
hence "normalize (x @ (y @ z)) = normalize (x @ normalize (y @ z))"
by -(rule normalize_append_cancel_to)
finally
show "x ⊗_F y ⊗ r[src f(r ⋆ ε \starrc f\^up>*) ⋅
x ⊗_F (y((r ⋆-^*\^<cdot( f 🚫 f^* ⋆ θ')) ⋅
by (auto simp add:free_group_def)

show "1_{F ∈ir F_{by (auto simp add:free_group_def)

fix x

assume "x ∈ carrier F"

thus "1_F, ff^<> w

by (auto simp add:free_group_def)

fix x

assume "x ∈ carrier F"

thus "x ⊗_{F_{y simp

by (auto simp add:free_group_def)

show "carrier F ⊆ Units F"

proof (simp add:free_group_def Units_def, rule subsetI)

fix x :: "'a word_g_i"

let ?x' = "inv_fg x"

assume "x ∈lists(UNIV×

hence "?x' ∈ lists(UNIV×gens) ∧ canceled ?x'"

by (auto elim:inv_fg_closure1 simp add:inv_fg_closure2)

moreover

have "normalize (?x' @ x) = []"

and "normalize (x @ ?x') = []"

by (auto simp add:inv_fg_cancel inv_fg_cancel2)

ultimately

have "∃y. y ∈ lists (UNIV × (f ⋆*) ⋆ θ') ⋅ (r ⋆-^*, f ⋆ w])) ⋅

canceled y ∧

normalize (y @ x) = [] ∧ normalize (x @ y) = []"

with ‹x ∈ {y∈lists(UNIV×gens). canceled y}›

show "x ∈ {y ∈ lists (UNIV × gens). canceled y ∧

(∃x. x ∈ a¹[f, f^*]) ⋅ f ⋆* ⋆') =

canceled x ∧

normalize (x @ y) = [] ∧ normalize (y @ x) = [])}"

by auto

qed

inv_is_inv_fg[simp]:

"x ∈ carrier F(r \<star f^\theta>') \<cdot( a>--^*, f ⋆ w])"

(rule group.inv_equality,auto simp add:free_group_is_group,auto simp add: free_group_def inv_fg_cancel inv_fg_cancel2 inv_fg_closure1 inv_fg_closure2)

‹The universal property›

‹Free Groups are important due to their universal property: Every map of

set of generators to another group can be extended uniquely to an

from the Free Group.›

insert (‹

where "ι g = [(False, g)]"

insert_closed:

"g ∈ gens ==> ι g ∈ carrier F a¹f,f\<>* (f ⋆* ⋆')"

by (auto simp add:insert_def free_group_def)

(in group) lift_gi

where "lift_gi f gi = (if fst gi then inv (f (snd gi)) else f (snd gi))"

(in group) lift_gi_closed:

assumes cl: "f ∈ gens → carrier G"

and "snd gi ∈ gens"

shows "lift_gi f gi ∈ carrier G"

assms by (auto simp add:lift_gi_def)

(in group) lift

where "lift f w = m_concat (map (lift_gi f) w)"

(in group) lift_nil[simp]: "lift f [] = 1"

by (auto simp add:lift_def)

(in group) lift_closed[simp]:

assumes cl: "f ∈ gens → carrier G"

and "x ∈ lists (UNIV × gens)"

shows "lift f x ∈ carrier hve "... = r ⋆ ( \<startar*) ⋆ a¹[f, f]"

-

have "set (map (lift_gi f) x) ⊆ carrier G"

using ‹x ∈ lists (UNIV × gens)› f"f^'] T0.antipar auto

by (auto simp add:lift_gi_closed[OF cl])

thus "lift f x ∈ carrier G"

by (auto simp add:lift_def)

(in group) lift_append[simp]:

assumes cl: "f ∈ gens → carrier G"

and "x ∈ lists (UNIV × (f ⋆*) ⋆') ⋅ a¹[f, fw])"

and "y ∈ lists (UNIV × gens)"

shows "lift f (x @ y) = lift f x ⊗ lift f y"

-

from ‹x ∈ lists (UNIV × gens)›t Ttia auto

have "set (map snd x) ⊆ gens" by auto

hence "set (map (lift_gi f) x) ⊆ carrier G"

by (induct x)(auto simp add:lift_gi_closed[OF cl])

moreover

from ‹y ∈

have "set (map snd y) ⊆ gens" by auto

hence "set (map (lift_gi f) y) ⊆ carrier G"

by (induct y)(auto simp add:lift_gi_closed[OF cl])

ultimately

show "lift f (x @ y) = lift f x ⊗ lift f y"

by (auto simp add:lift_def m_assoc simp del:set_map foldr_append)

(in group) lift_cancels_to:

assumes "cancelto x y"

and "x ∈ lists (UNIV × gens)"

and cl: "f ∈ gens → carrier G"

shows "lift f x = lift f y"

assms

cancels_to_def

(induct rule:rtranclp_induct)

case (step y z)

from ‹

and ‹x ∈ lists (UNIV × gens)›

have "y ∈

by -(rule cancels_to_preserves_generators, simp add:cancels_to_def)

hence "lift f x = lift f y"

using step by auto

also

from ‹cancels_to_1 y z›

obtain ys1 y1 y2 ys2

where y: "y = ys1 @ y1 # y2 # ys2"

and "z = ys1 @ ys2"

and "canceling y1 y2"

by (rule cancels_to_1_unfold)

have "lift f y = lift f (ys1 @ [y1] @ [y2] @ ys2)"

using y by simp

also

from y and cl and ‹y ∈ lists (UNIV × gens)›

have "lift f (ys1 @ [y1] @ [y2] @ ys2)

= lift f ys1 ⊗ a¹[f, fw]) ⋅* ⋆ w]"

by (auto intro:lift_append[OF cl] simp del: append_Cons simp add:m_assoc iff:lists_eq_set)

also

from cl[THEN funcset_image]

and y and ‹y ∈ lists (UNIV × gens)›usincomp_assoc by si

and ‹canceling y1 y2›

have "(lift f [y1] ⊗

by (auto simp add:lift_def lift_gi_def canceling_def iff:lists_eq_set)

hence "lift f ys1 ⊗ (lift f [y1] ⊗ lift f [y2]) ⊗ lift f ys2

= lift f ys1 ⊗ 1 ⊗ lift f ys2"

by simp

also

from y and ‹y ∈ lists (UNIV × gens)›

and cl

have "lift f ys1 ⊗ a¹f, \<^>,cdot> \a>[r, f, f^* ⋆ f ⋆ w]"

by (auto intro:lift_append iff:lists_eq_set)

also

from ‹z = ys1 @ ys2›

have "lift f (ys1 @ ys2) = lift f z" by simp

finally show "lift f x = lift f z" .

auto

(in group) lift_is_hom:

assumes cl: "f ∈ carrier G"

shows "lift f ∈ hom F G"

-

{

fix x

assume "x ∈ carrier F"

hence "x ∈ lists (UNIV × gens)"

unfolding free_group_def by simp

hence "lift f x ∈ carrier G"

by (induct x, auto simp add:lift_def lift_gi_closed[OF cl])

}

moreover

{ fix x

assume "x ∈ carrier F"

fix y

assume "y ∈ carrier F"

from ‹x ∈ carrier F_{r[src f((r ⋆ θ (r ⋆ ⋆ w)) ⋅

have "x ∈ lists (UNIV × gens)" and "y ∈ lists (UNIV × gens)"

by (auto simp add:free_group_def)

have "canr \<star\-^*, f ⋆ af,\^up> \<>f w]"

from ‹x ∈ lists (UNIV × gens)› and ‹y ∈proof

and lift_cancels_to[THEN sym, OF ‹cancels_to (x @ y) (normalize (x @ y))›] and cl

have "lift f (x ⊗_{ε src f(r ⋆ fθ

by (auto simp add:free_group_def iff:lists_eq_set)

also

from ‹x ∈ lists (UNIV × gens)› and ‹ src fθ (r ⋆ f ⋆

have "lift f (x @ y) = lift f x ⊗ lift f y"

by simp

finally

java.lang.NullPointerException

}

ultimately

show "lift f ∈ hom F_{"(r \star ε ⋆*) ⋅ (f ⋆*) ⋆') =

by auto

gens_span_free_group:

"⟨ι ` gens⟩_F ⋆*) \<cdot *) ⋆')"

interpret group "F" by (rule free_group_is_group)

show "⟨ι ` gens⟩ by p

by(rule gen_span_closed, auto simp add:insert_def free_group_def)

show "carrier F ⊆ ⟨ι. = \ ε ⋆

proof

fix x

java.lang.NullPointerException

proof(induct x)

case Nil

have "one F ∈ ⟨

by simp

thus "[] ∈ ⟨ι ` gens⟩_{y ato

by (simp add:free_group_def)

next

case (Cons a x)

from ‹a # x ∈ carrier F_{(src f^theta') ⋅ f ⋆

have "x ∈ carrier F"

by (auto intro:cons_canceled simp add:free_group_def)

hence "x ∈ \<langlenterchange*" ε\theta"f<tar w"]

using Cons by simp

moreover

from ‹ carrier F_{coe

have "snd a ∈ gens"

by (auto simp add:free_group_def)

hence isa: "ι (snd a) ∈ ⟨ι ` gens⟩

by (auto simp add:insert_def intro:gen_gens)

have "[a] ∈ ⟨ι ` gens⟩

proof(cases "fst a")

case False

hence "[a] = ι (snd a)" by (cases a, auto simp add:insert_def)

with isa show "[a] ∈ src fθ (r ⋆ ⋆)

next

case True

snd a ∈ gens}›

have "ι (snd a) ∈ carrier F"

by (auto simp add:free_group_def insert_def)

with True

have "[a] = inv_F (ι (snd a))"

by (cases a, auto simp add:insert_def inv_fg_def inv1_def)

moreover

from isa

java.lang.NullPointerException

by (auto intro:gen_inv)

ultimately

show "[a] ∈ ⟨ι ` gens⟩_{F

by simp

qed

ultimately

have "mult F [a] x ∈ r[src ^> (r ⋆ src f^* ⋆ θ (r ⋆ ⋆ w) ⋅

by (auto intro:gen_mult)

with

‹a # x ∈ a¹[f, fw]) ⋅[r, f, ff \star w]"

show "a # x ∈ ⟨ι ` gens⟩_{F

qed

qed

(in group) lift_is_unique:

assumes "group G"

and cl: "f ∈ gens → carrier G"

java.lang.NullPointerException

and "∀ g ∈ gens. h (ι g) = f g"

shows "∀x ∈ carrier F

gens_span_free_group[THEN sym]

(rule hom_unique_on_span[of "F" G])

show "group F ⋆* ⋆ w) ⋅ a[f(g ⋆ w) =

show "group G" by fact

show "ι ` gens ⊆ carrier F f) ⋆<^up* ((r ⋆ η⋆ (ρ trg w ⋆

by(auto intro:insert_closed)

show "h ∈ hom F G" by fact

show "lift f ∈ hom F

from ‹∀g∈ gens. h (ι g) = f g› and cl[THEN funcset_image]

g∈ ι ` gens. h g = lift f g"

by(auto simp add:insert_def lift_def lift_gi_def)}}}}}}}}}}}

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Beweissystem der NASA

Beweissystem Isabelle

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Cephes Mathematical Library

Wiener Entwicklungsmethode

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