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Quotient ring (#81)

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Patrick Stevens
2019-11-21 07:28:25 +00:00
committed by GitHub
parent d4f51a3efe
commit b33baa5fb7
12 changed files with 125 additions and 64 deletions
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2
Groups/Subgroups/Normal/Definition.agda
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@@ -21,5 +21,5 @@ open import Agda.Primitive using (Level; lzero; lsuc; _⊔_)
module Groups.Subgroups.Normal.Definition {a b : _} {A : Set a} {S : Setoid {a} {b} A} {_+_ : A → A → A} (G : Group S _+_) where
normalSubgroup : {c : _} {pred : A → Set c} (sub : subgroup G pred) → Set (a ⊔ c)
normalSubgroup : {c : _} {pred : A → Set c} (sub : Subgroup G pred) → Set (a ⊔ c)
normalSubgroup {pred = pred} sub = {g k : A} → pred k → pred (g + (k + Group.inverse G g))

14
Groups/Subgroups/Normal/Lemmas.agda
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@@ -64,11 +64,11 @@ groupKernelGroupPred {T = T} G {H = H} {f = f} hom a = Setoid._∼_ T (f a) (Gro
groupKernelGroupPredWd : {a b c d : _} {A : Set a} {B : Set c} {S : Setoid {a} {b} A} {T : Setoid {c} {d} B} {_·A_ : A → A → A} {_·B_ : B → B → B} (G : Group S _·A_) {H : Group T _·B_} {f : A → B} (hom : GroupHom G H f) → {x y : A} → (Setoid._∼_ S x y) → (groupKernelGroupPred G hom x → groupKernelGroupPred G hom y)
groupKernelGroupPredWd {S = S} {T = T} G hom {x} {y} x=y fx=0 = Equivalence.transitive (Setoid.eq T) (GroupHom.wellDefined hom (Equivalence.symmetric (Setoid.eq S) x=y)) fx=0
groupKernelGroupIsSubgroup : {a b c d : _} {A : Set a} {B : Set c} {S : Setoid {a} {b} A} {T : Setoid {c} {d} B} {_·A_ : A → A → A} {_·B_ : B → B → B} (G : Group S _·A_) {H : Group T _·B_} {f : A → B} (hom : GroupHom G H f) → subgroup G (groupKernelGroupPred G hom)
_&_&_.one (_&&_.snd (groupKernelGroupIsSubgroup {S = S} {T = T} G {H = H} hom)) g=0 h=0 = Equivalence.transitive (Setoid.eq T) (GroupHom.groupHom hom) (Equivalence.transitive (Setoid.eq T) (Group.+WellDefined H g=0 h=0) (Group.identLeft H))
_&_&_.two (_&&_.snd (groupKernelGroupIsSubgroup G hom)) = imageOfIdentityIsIdentity hom
_&_&_.three (_&&_.snd (groupKernelGroupIsSubgroup {S = S} {T = T} G {H = H} hom)) g=0 = Equivalence.transitive (Setoid.eq T) (homRespectsInverse hom) (Equivalence.transitive (Setoid.eq T) (inverseWellDefined H g=0) (invIdent H))
_&&_.fst (groupKernelGroupIsSubgroup G hom) = groupKernelGroupPredWd G hom
groupKernelGroupIsSubgroup : {a b c d : _} {A : Set a} {B : Set c} {S : Setoid {a} {b} A} {T : Setoid {c} {d} B} {_·A_ : A → A → A} {_·B_ : B → B → B} (G : Group S _·A_) {H : Group T _·B_} {f : A → B} (hom : GroupHom G H f) → Subgroup G (groupKernelGroupPred G hom)
Subgroup.closedUnderPlus (groupKernelGroupIsSubgroup {S = S} {T = T} G {H = H} hom) g=0 h=0 = Equivalence.transitive (Setoid.eq T) (GroupHom.groupHom hom) (Equivalence.transitive (Setoid.eq T) (Group.+WellDefined H g=0 h=0) (Group.identLeft H))
Subgroup.containsIdentity (groupKernelGroupIsSubgroup G hom) = imageOfIdentityIsIdentity hom
Subgroup.closedUnderInverse (groupKernelGroupIsSubgroup {S = S} {T = T} G {H = H} hom) g=0 = Equivalence.transitive (Setoid.eq T) (homRespectsInverse hom) (Equivalence.transitive (Setoid.eq T) (inverseWellDefined H g=0) (invIdent H))
Subgroup.isSubset (groupKernelGroupIsSubgroup G hom) = groupKernelGroupPredWd G hom
groupKernelGroupIsNormalSubgroup : {a b c d : _} {A : Set a} {B : Set c} {S : Setoid {a} {b} A} {T : Setoid {c} {d} B} {_·A_ : A → A → A} {_·B_ : B → B → B} (G : Group S _·A_) {H : Group T _·B_} {f : A → B} (hom : GroupHom G H f) → normalSubgroup G (groupKernelGroupIsSubgroup G hom)
groupKernelGroupIsNormalSubgroup {T = T} G {H = H} hom k=0 = transitive groupHom (transitive (+WellDefined reflexive groupHom) (transitive (+WellDefined reflexive (transitive (+WellDefined k=0 reflexive) identLeft)) (transitive (symmetric groupHom) (transitive (wellDefined (Group.invRight G)) (imageOfIdentityIsIdentity hom)))))
@@ -78,8 +78,8 @@ groupKernelGroupIsNormalSubgroup {T = T} G {H = H} hom k=0 = transitive groupHom
open Equivalence eq
open GroupHom hom
abelianGroupSubgroupIsNormal : {a b c : _} {A : Set a} {B : Set b} {S : Setoid {a} {b} A} {_+_ : A → A → A} {G : Group S _+_} {pred : A → Set c} → (s : subgroup G pred) → AbelianGroup G → normalSubgroup G s
abelianGroupSubgroupIsNormal {S = S} {_+_ = _+_} {G = G} (predWd ,, record { one = respectsPlus ; two = respectsId ; three = respectsInv }) abelian {k} {l} prK = predWd (transitive (transitive (transitive (symmetric identLeft) (+WellDefined (symmetric invRight) reflexive)) (symmetric +Associative)) (+WellDefined reflexive commutative)) prK
abelianGroupSubgroupIsNormal : {a b c : _} {A : Set a} {S : Setoid {a} {b} A} {_+_ : A → A → A} {G : Group S _+_} {pred : A → Set c} → (s : Subgroup G pred) → AbelianGroup G → normalSubgroup G s
abelianGroupSubgroupIsNormal {S = S} {_+_ = _+_} {G = G} record { isSubset = predWd ; closedUnderPlus = respectsPlus ; containsIdentity = respectsId ; closedUnderInverse = respectsInv } abelian {k} {l} prK = predWd (transitive (transitive (transitive (symmetric identLeft) (+WellDefined (symmetric invRight) reflexive)) (symmetric +Associative)) (+WellDefined reflexive commutative)) prK
where
open Group G
open AbelianGroup abelian