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| author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Sat, 17 Aug 2013 21:09:34 +0900 |
| parents | 5f331dfc000b |
| children | 0be3e0a49cca |
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module universal-mapping where -- Shinji KONO <kono@ie.u-ryukyu.ac.jp> open import Category -- https://github.com/konn/category-agda open import Level open import HomReasoning open Functor id1 : ∀{c₁ c₂ ℓ : Level} (A : Category c₁ c₂ ℓ) (a : Obj A ) → Hom A a a id1 A a = (Id {_} {_} {_} {A} a) record IsUniversalMapping {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') ( U : Functor B A ) ( F : Obj A → Obj B ) ( η : (a : Obj A) → Hom A a ( FObj U (F a) ) ) ( _* : { a : Obj A}{ b : Obj B} → ( Hom A a (FObj U b) ) → Hom B (F a ) b ) : Set (suc (c₁ ⊔ c₂ ⊔ ℓ ⊔ c₁' ⊔ c₂' ⊔ ℓ' )) where field universalMapping : {a' : Obj A} { b' : Obj B } → { f : Hom A a' (FObj U b') } → A [ A [ FMap U ( f * ) o η a' ] ≈ f ] uniquness : {a' : Obj A} { b' : Obj B } → { f : Hom A a' (FObj U b') } → { g : Hom B (F a') b' } → A [ A [ FMap U g o η a' ] ≈ f ] → B [ f * ≈ g ] record UniversalMapping {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') ( U : Functor B A ) ( F : Obj A → Obj B ) ( η : (a : Obj A) → Hom A a ( FObj U (F a) ) ) : Set (suc (c₁ ⊔ c₂ ⊔ ℓ ⊔ c₁' ⊔ c₂' ⊔ ℓ' )) where infixr 11 _* field _* : { a : Obj A}{ b : Obj B} → ( Hom A a (FObj U b) ) → Hom B (F a ) b isUniversalMapping : IsUniversalMapping A B U F η _* open NTrans open import Category.Cat record IsAdjunction {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') ( U : Functor B A ) ( F : Functor A B ) ( η : NTrans A A identityFunctor ( U ○ F ) ) ( ε : NTrans B B ( F ○ U ) identityFunctor ) : Set (suc (c₁ ⊔ c₂ ⊔ ℓ ⊔ c₁' ⊔ c₂' ⊔ ℓ' )) where field adjoint1 : { b' : Obj B } → A [ A [ ( FMap U ( TMap ε b' )) o ( TMap η ( FObj U b' )) ] ≈ id1 A (FObj U b') ] adjoint2 : {a' : Obj A} → B [ B [ ( TMap ε ( FObj F a' )) o ( FMap F ( TMap η a' )) ] ≈ id1 B (FObj F a') ] record Adjunction {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') ( U : Functor B A ) ( F : Functor A B ) ( η : NTrans A A identityFunctor ( U ○ F ) ) ( ε : NTrans B B ( F ○ U ) identityFunctor ) : Set (suc (c₁ ⊔ c₂ ⊔ ℓ ⊔ c₁' ⊔ c₂' ⊔ ℓ' )) where field isAdjunction : IsAdjunction A B U F η ε -- -- Adjunction yields solution of universal mapping -- -- open Adjunction open UniversalMapping Adj2UM : {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') { U : Functor B A } { F : Functor A B } { η : NTrans A A identityFunctor ( U ○ F ) } { ε : NTrans B B ( F ○ U ) identityFunctor } → Adjunction A B U F η ε → UniversalMapping A B U (FObj F) (TMap η) Adj2UM A B {U} {F} {η} {ε} adj = record { _* = solution ; isUniversalMapping = record { universalMapping = universalMapping; uniquness = uniqness } } where solution : { a : Obj A} { b : Obj B} → ( f : Hom A a (FObj U b) ) → Hom B (FObj F a ) b solution {_} {b} f = B [ TMap ε b o FMap F f ] universalMapping : {a' : Obj A} { b' : Obj B } → { f : Hom A a' (FObj U b') } → A [ A [ FMap U ( solution f) o TMap η a' ] ≈ f ] universalMapping {a} {b} {f} = let open ≈-Reasoning (A) in begin FMap U ( solution f) o TMap η a ≈⟨⟩ FMap U ( B [ TMap ε b o FMap F f ] ) o TMap η a ≈⟨ car (distr U ) ⟩ ( (FMap U (TMap ε b)) o (FMap U ( FMap F f )) ) o TMap η a ≈⟨ sym assoc ⟩ (FMap U (TMap ε b)) o ((FMap U ( FMap F f )) o TMap η a ) ≈⟨ cdr (nat η) ⟩ (FMap U (TMap ε b)) o ((TMap η (FObj U b )) o f ) ≈⟨ assoc ⟩ ((FMap U (TMap ε b)) o (TMap η (FObj U b))) o f ≈⟨ car ( IsAdjunction.adjoint1 ( isAdjunction adj)) ⟩ id (FObj U b) o f ≈⟨ idL ⟩ f ∎ lemma1 : (a : Obj A) ( b : Obj B ) ( f : Hom A a (FObj U b) ) → ( g : Hom B (FObj F a) b) → A [ A [ FMap U g o TMap η a ] ≈ f ] → B [ (FMap F (A [ FMap U g o TMap η a ] )) ≈ FMap F f ] lemma1 a b f g k = IsFunctor.≈-cong (isFunctor F) k uniqness : {a' : Obj A} { b' : Obj B } → { f : Hom A a' (FObj U b') } → { g : Hom B (FObj F a') b'} → A [ A [ FMap U g o TMap η a' ] ≈ f ] → B [ solution f ≈ g ] uniqness {a} {b} {f} {g} k = let open ≈-Reasoning (B) in begin solution f ≈⟨⟩ TMap ε b o FMap F f ≈⟨ cdr (sym ( lemma1 a b f g k )) ⟩ TMap ε b o FMap F ( A [ FMap U g o TMap η a ] ) ≈⟨ cdr (distr F ) ⟩ TMap ε b o ( FMap F ( FMap U g) o FMap F ( TMap η a ) ) ≈⟨ assoc ⟩ ( TMap ε b o FMap F ( FMap U g) ) o FMap F ( TMap η a ) ≈⟨ sym ( car ( nat ε )) ⟩ ( g o TMap ε ( FObj F a) ) o FMap F ( TMap η a ) ≈⟨ sym assoc ⟩ g o ( TMap ε ( FObj F a) o FMap F ( TMap η a ) ) ≈⟨ cdr ( IsAdjunction.adjoint2 ( isAdjunction adj )) ⟩ g o id (FObj F a) ≈⟨ idR ⟩ g ∎ -- -- -- Universal mapping yields Adjunction -- -- -- -- F is an functor -- FunctorF : {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') { U : Functor B A } { F : Obj A → Obj B } { η : (a : Obj A) → Hom A a ( FObj U (F a) ) } → UniversalMapping A B U F η → Functor A B FunctorF A B {U} {F} {η} um = record { FObj = F; FMap = myFMap ; isFunctor = myIsFunctor } where myFMap : {a b : Obj A} → Hom A a b → Hom B (F a) (F b) myFMap f = (_* um) (A [ η (Category.cod A f ) o f ]) lemma-id1 : {a : Obj A} → A [ A [ FMap U (id1 B (F a)) o η a ] ≈ (A [ (η a) o (id1 A a) ]) ] lemma-id1 {a} = let open ≈-Reasoning (A) in begin FMap U (id1 B (F a)) o η a ≈⟨ ( car ( IsFunctor.identity ( isFunctor U ))) ⟩ id (FObj U ( F a )) o η a ≈⟨ idL ⟩ η a ≈⟨ sym idR ⟩ η a o id a ∎ lemma-id : {a : Obj A} → B [ ( (_* um) (A [ (η a) o (id1 A a)] )) ≈ (id1 B (F a)) ] lemma-id {a} = ( IsUniversalMapping.uniquness ( isUniversalMapping um ) ) lemma-id1 lemma-cong2 : (a b : Obj A) (f g : Hom A a b) → A [ f ≈ g ] → A [ A [ FMap U ((_* um) (A [ η b o g ]) ) o η a ] ≈ A [ η b o f ] ] lemma-cong2 a b f g eq = let open ≈-Reasoning (A) in begin ( FMap U ((_* um) (A [ η b o g ]) )) o η a ≈⟨ ( IsUniversalMapping.universalMapping ( isUniversalMapping um )) ⟩ η b o g ≈⟨ ( IsCategory.o-resp-≈ ( Category.isCategory A ) (sym eq) (refl-hom) ) ⟩ η b o f ∎ lemma-cong1 : (a b : Obj A) (f g : Hom A a b) → A [ f ≈ g ] → B [ (_* um) (A [ η b o f ] ) ≈ (_* um) (A [ η b o g ]) ] lemma-cong1 a b f g eq = ( IsUniversalMapping.uniquness ( isUniversalMapping um ) ) ( lemma-cong2 a b f g eq ) lemma-cong : {a b : Obj A} {f g : Hom A a b} → A [ f ≈ g ] → B [ myFMap f ≈ myFMap g ] lemma-cong {a} {b} {f} {g} eq = lemma-cong1 a b f g eq lemma-distr2 : (a b c : Obj A) (f : Hom A a b) (g : Hom A b c) → A [ A [ FMap U (B [(_* um) (A [ η c o g ]) o (_* um)( A [ η b o f ]) ]) o η a ] ≈ (A [ η c o A [ g o f ] ]) ] lemma-distr2 a b c f g = let open ≈-Reasoning (A) in begin ( FMap U (B [(_* um) (A [ η c o g ]) o (_* um)( A [ η b o f ]) ] ) ) o η a ≈⟨ car (distr U ) ⟩ (( FMap U ((_* um) (A [ η c o g ])) o ( FMap U ((_* um)( A [ η b o f ])))) ) o η a ≈⟨ sym assoc ⟩ ( FMap U ((_* um) (A [ η c o g ])) o (( FMap U ((_* um)( A [ η b o f ])))) o η a ) ≈⟨ cdr ( IsUniversalMapping.universalMapping ( isUniversalMapping um )) ⟩ ( FMap U ((_* um) (A [ η c o g ])) o ( η b o f) ) ≈⟨ assoc ⟩ ( FMap U ((_* um) (A [ η c o g ])) o η b) o f ≈⟨ car ( IsUniversalMapping.universalMapping ( isUniversalMapping um )) ⟩ ( η c o g ) o f ≈⟨ sym assoc ⟩ η c o ( g o f ) ∎ lemma-distr1 : (a b c : Obj A) (f : Hom A a b) (g : Hom A b c) → B [ (_* um) (A [ η c o A [ g o f ] ]) ≈ (B [(_* um) (A [ η c o g ]) o (_* um)( A [ η b o f ]) ] )] lemma-distr1 a b c f g = ( IsUniversalMapping.uniquness ( isUniversalMapping um )) (lemma-distr2 a b c f g ) lemma-distr : {a b c : Obj A} {f : Hom A a b} {g : Hom A b c} → B [ myFMap (A [ g o f ]) ≈ (B [ myFMap g o myFMap f ] )] lemma-distr {a} {b} {c} {f} {g} = lemma-distr1 a b c f g myIsFunctor : IsFunctor A B F myFMap myIsFunctor = record { ≈-cong = lemma-cong ; identity = lemma-id ; distr = lemma-distr } -- -- naturality of η -- nat-η : {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') { U : Functor B A } { F : Obj A → Obj B } { η : (a : Obj A) → Hom A a ( FObj U (F a) ) } → (um : UniversalMapping A B U F η ) → NTrans A A identityFunctor ( U ○ FunctorF A B um ) nat-η A B {U} {F} {η} um = record { TMap = η ; isNTrans = myIsNTrans } where F' : Functor A B F' = FunctorF A B um commute : {a b : Obj A} {f : Hom A a b} → A [ A [ (FMap U (FMap F' f)) o ( η a ) ] ≈ A [ (η b ) o f ] ] commute {a} {b} {f} = let open ≈-Reasoning (A) in begin (FMap U (FMap F' f)) o ( η a ) ≈⟨⟩ (FMap U ((_* um) (A [ η b o f ]))) o ( η a ) ≈⟨ (IsUniversalMapping.universalMapping ( isUniversalMapping um )) ⟩ (η b ) o f ∎ myIsNTrans : IsNTrans A A identityFunctor ( U ○ F' ) η myIsNTrans = record { commute = commute } nat-ε : {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') { U : Functor B A } { F : Obj A → Obj B } { η : (a : Obj A) → Hom A a ( FObj U (F a) ) } → (um : UniversalMapping A B U F η ) → NTrans B B ( FunctorF A B um ○ U) identityFunctor nat-ε A B {U} {F} {η} um = record { TMap = ε ; isNTrans = myIsNTrans } where F' : Functor A B F' = FunctorF A B um ε : ( b : Obj B ) → Hom B ( FObj F' ( FObj U b) ) b ε b = (_* um) ( id1 A (FObj U b)) lemma-nat1 : (a b : Obj B) (f : Hom B a b ) → A [ A [ FMap U ( B [ (um *) (id1 A (FObj U b)) o ((um *) (A [ η (FObj U b) o FMap U f ])) ] ) o η (FObj U a) ] ≈ A [ FMap U f o id1 A (FObj U a) ] ] lemma-nat1 a b f = let open ≈-Reasoning (A) in begin FMap U ( B [ (um *) (id1 A (FObj U b)) o ((um *) ( η (FObj U b) o FMap U f )) ] ) o η (FObj U a) ≈⟨ car ( distr U ) ⟩ ( FMap U ((um *) (id1 A (FObj U b))) o FMap U ((um *) ( η (FObj U b) o FMap U f )) ) o η (FObj U a) ≈⟨ sym assoc ⟩ FMap U ((um *) (id1 A (FObj U b))) o ( FMap U ((um *) ( η (FObj U b) o FMap U f ))) o η (FObj U a) ≈⟨ cdr ((IsUniversalMapping.universalMapping ( isUniversalMapping um )) ) ⟩ FMap U ((um *) (id1 A (FObj U b))) o ( η (FObj U b) o FMap U f ) ≈⟨ assoc ⟩ (FMap U ((um *) (id1 A (FObj U b))) o η (FObj U b)) o FMap U f ≈⟨ car ((IsUniversalMapping.universalMapping ( isUniversalMapping um )) ) ⟩ id1 A (FObj U b) o FMap U f ≈⟨ idL ⟩ FMap U f ≈⟨ sym idR ⟩ FMap U f o id (FObj U a) ∎ lemma-nat2 : (a b : Obj B) (f : Hom B a b ) → A [ A [ FMap U ( B [ f o ((um *) (id1 A (FObj U a ))) ] ) o η (FObj U a) ] ≈ A [ FMap U f o id1 A (FObj U a) ] ] lemma-nat2 a b f = let open ≈-Reasoning (A) in begin FMap U ( B [ f o ((um *) (id1 A (FObj U a ))) ]) o η (FObj U a) ≈⟨ car ( distr U ) ⟩ (FMap U f o FMap U ((um *) (id1 A (FObj U a )))) o η (FObj U a) ≈⟨ sym assoc ⟩ FMap U f o ( FMap U ((um *) (id1 A (FObj U a ))) o η (FObj U a) ) ≈⟨ cdr ( IsUniversalMapping.universalMapping ( isUniversalMapping um)) ⟩ FMap U f o id (FObj U a ) ∎ commute : {a b : Obj B} {f : Hom B a b } → B [ B [ f o (ε a) ] ≈ B [(ε b) o (FMap F' (FMap U f)) ] ] commute {a} {b} {f} = let open ≈-Reasoning (B) in sym ( begin ε b o (FMap F' (FMap U f)) ≈⟨⟩ ε b o ((_* um) (A [ η (FObj U b) o (FMap U f) ])) ≈⟨⟩ ((_* um) ( id1 A (FObj U b))) o ((_* um) (A [ η (FObj U b) o (FMap U f) ])) ≈⟨ sym ( ( IsUniversalMapping.uniquness ( isUniversalMapping um ) (lemma-nat1 a b f))) ⟩ (_* um) ( A [ FMap U f o id1 A (FObj U a) ] ) ≈⟨ (IsUniversalMapping.uniquness ( isUniversalMapping um ) (lemma-nat2 a b f)) ⟩ f o ((_* um) ( id1 A (FObj U a))) ≈⟨⟩ f o (ε a) ∎ ) myIsNTrans : IsNTrans B B ( F' ○ U ) identityFunctor ε myIsNTrans = record { commute = commute } ------ -- -- Adjunction Construction from Universal Mapping -- ----- UMAdjunction : {c₁ c₂ ℓ c₁' c₂' ℓ' : Level} (A : Category c₁ c₂ ℓ) (B : Category c₁' c₂' ℓ') ( U : Functor B A ) ( F' : Obj A → Obj B ) ( η' : (a : Obj A) → Hom A a ( FObj U (F' a) ) ) → (um : UniversalMapping A B U F' η' ) → Adjunction A B U (FunctorF A B um) (nat-η A B um) (nat-ε A B um) UMAdjunction A B U F' η' um = record { isAdjunction = record { adjoint1 = adjoint1 ; adjoint2 = adjoint2 } } where F : Functor A B F = FunctorF A B um η : NTrans A A identityFunctor ( U ○ F ) η = nat-η A B um ε : NTrans B B ( F ○ U ) identityFunctor ε = nat-ε A B um adjoint1 : { b : Obj B } → A [ A [ ( FMap U ( TMap ε b )) o ( TMap η ( FObj U b )) ] ≈ id1 A (FObj U b) ] adjoint1 {b} = let open ≈-Reasoning (A) in begin FMap U ( TMap ε b ) o TMap η ( FObj U b ) ≈⟨⟩ FMap U ((_* um) ( id1 A (FObj U b))) o η' ( FObj U b ) ≈⟨ IsUniversalMapping.universalMapping ( isUniversalMapping um ) ⟩ id (FObj U b) ∎ lemma-adj1 : (a : Obj A) → A [ A [ FMap U ((B [((_* um) ( id1 A (FObj U ( FObj F a )))) o (_* um) (A [ η' (FObj U ( FObj F a )) o ( η' a ) ]) ])) o η' a ] ≈ (η' a) ] lemma-adj1 a = let open ≈-Reasoning (A) in begin FMap U ((B [((_* um) ( id1 A (FObj U ( FObj F a )))) o (_* um) (A [ η' (FObj U ( FObj F a )) o ( η' a ) ]) ])) o η' a ≈⟨ car (distr U) ⟩ (FMap U ((_* um) ( id1 A (FObj U ( FObj F a)))) o FMap U ((_* um) (A [ η' (FObj U ( FObj F a )) o ( η' a ) ]))) o η' a ≈⟨ sym assoc ⟩ FMap U ((_* um) ( id1 A (FObj U ( FObj F a)))) o ( FMap U ((_* um) (A [ η' (FObj U ( FObj F a )) o ( η' a ) ])) o η' a ) ≈⟨ cdr (IsUniversalMapping.universalMapping ( isUniversalMapping um)) ⟩ FMap U ((_* um) ( id1 A (FObj U ( FObj F a)))) o ( η' (FObj U ( FObj F a )) o ( η' a ) ) ≈⟨ assoc ⟩ (FMap U ((_* um) ( id1 A (FObj U ( FObj F a)))) o ( η' (FObj U ( FObj F a )))) o ( η' a ) ≈⟨ car (IsUniversalMapping.universalMapping ( isUniversalMapping um)) ⟩ id (FObj U ( FObj F a)) o ( η' a ) ≈⟨ idL ⟩ η' a ∎ lemma-adj2 : (a : Obj A) → A [ A [ FMap U (id1 B (FObj F a)) o η' a ] ≈ η' a ] lemma-adj2 a = let open ≈-Reasoning (A) in begin FMap U (id1 B (FObj F a)) o η' a ≈⟨ car ( IsFunctor.identity ( isFunctor U)) ⟩ id (FObj U (FObj F a)) o η' a ≈⟨ idL ⟩ η' a ∎ adjoint2 : {a : Obj A} → B [ B [ ( TMap ε ( FObj F a )) o ( FMap F ( TMap η a )) ] ≈ id1 B (FObj F a) ] adjoint2 {a} = let open ≈-Reasoning (B) in begin TMap ε ( FObj F a ) o FMap F ( TMap η a ) ≈⟨⟩ ((_* um) ( id1 A (FObj U ( FObj F a )))) o (_* um) (A [ η' (FObj U ( FObj F a )) o ( η' a ) ]) ≈⟨ sym ( ( IsUniversalMapping.uniquness ( isUniversalMapping um ) (lemma-adj1 a))) ⟩ (_* um)( η' a ) ≈⟨ IsUniversalMapping.uniquness ( isUniversalMapping um ) (lemma-adj2 a) ⟩ id1 B (FObj F a) ∎ -- done!