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| Type | Label | Description |
|---|---|---|
| Statement | ||
| Syntax | ccofu 17901 | Extend class notation with functor composition. |
| class ∘func | ||
| Syntax | cresf 17902 | Extend class notation to include restriction of a functor to a subcategory. |
| class ↾f | ||
| Definition | df-func 17903* | Function returning all the functors from a category 𝑡 to a category 𝑢. Definition 3.17 of [Adamek] p. 29, and definition in [Lang] p. 62 ("covariant functor"). Intuitively a functor associates any morphism of 𝑡 to a morphism of 𝑢, any object of 𝑡 to an object of 𝑢, and respects the identity, the composition, the domain and the codomain. Here to capture the idea that a functor associates any object of 𝑡 to an object of 𝑢 we write it associates any identity of 𝑡 to an identity of 𝑢 which simplifies the definition. According to remark 3.19 in [Adamek] p. 30, "a functor F : A -> B is technically a family of functions; one from Ob(A) to Ob(B) [here: f, called "the object part" in the following], and for each pair (A,A') of A-objects, one from hom(A,A') to hom(FA, FA') [here: g, called "the morphism part" in the following]". (Contributed by FL, 10-Feb-2008.) (Revised by Mario Carneiro, 2-Jan-2017.) |
| ⊢ Func = (𝑡 ∈ Cat, 𝑢 ∈ Cat ↦ {〈𝑓, 𝑔〉 ∣ [(Base‘𝑡) / 𝑏](𝑓:𝑏⟶(Base‘𝑢) ∧ 𝑔 ∈ X𝑧 ∈ (𝑏 × 𝑏)(((𝑓‘(1st ‘𝑧))(Hom ‘𝑢)(𝑓‘(2nd ‘𝑧))) ↑m ((Hom ‘𝑡)‘𝑧)) ∧ ∀𝑥 ∈ 𝑏 (((𝑥𝑔𝑥)‘((Id‘𝑡)‘𝑥)) = ((Id‘𝑢)‘(𝑓‘𝑥)) ∧ ∀𝑦 ∈ 𝑏 ∀𝑧 ∈ 𝑏 ∀𝑚 ∈ (𝑥(Hom ‘𝑡)𝑦)∀𝑛 ∈ (𝑦(Hom ‘𝑡)𝑧)((𝑥𝑔𝑧)‘(𝑛(〈𝑥, 𝑦〉(comp‘𝑡)𝑧)𝑚)) = (((𝑦𝑔𝑧)‘𝑛)(〈(𝑓‘𝑥), (𝑓‘𝑦)〉(comp‘𝑢)(𝑓‘𝑧))((𝑥𝑔𝑦)‘𝑚))))}) | ||
| Definition | df-idfu 17904* | Define the identity functor. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ idfunc = (𝑡 ∈ Cat ↦ ⦋(Base‘𝑡) / 𝑏⦌〈( I ↾ 𝑏), (𝑧 ∈ (𝑏 × 𝑏) ↦ ( I ↾ ((Hom ‘𝑡)‘𝑧)))〉) | ||
| Definition | df-cofu 17905* | Define the composition of two functors. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ ∘func = (𝑔 ∈ V, 𝑓 ∈ V ↦ 〈((1st ‘𝑔) ∘ (1st ‘𝑓)), (𝑥 ∈ dom dom (2nd ‘𝑓), 𝑦 ∈ dom dom (2nd ‘𝑓) ↦ ((((1st ‘𝑓)‘𝑥)(2nd ‘𝑔)((1st ‘𝑓)‘𝑦)) ∘ (𝑥(2nd ‘𝑓)𝑦)))〉) | ||
| Definition | df-resf 17906* | Define the restriction of a functor to a subcategory (analogue of df-res 5697). (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ ↾f = (𝑓 ∈ V, ℎ ∈ V ↦ 〈((1st ‘𝑓) ↾ dom dom ℎ), (𝑥 ∈ dom ℎ ↦ (((2nd ‘𝑓)‘𝑥) ↾ (ℎ‘𝑥)))〉) | ||
| Theorem | relfunc 17907 | The set of functors is a relation. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ Rel (𝐷 Func 𝐸) | ||
| Theorem | funcrcl 17908 | Reverse closure for a functor. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝐹 ∈ (𝐷 Func 𝐸) → (𝐷 ∈ Cat ∧ 𝐸 ∈ Cat)) | ||
| Theorem | isfunc 17909* | Value of the set of functors between two categories. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐶 = (Base‘𝐸) & ⊢ 𝐻 = (Hom ‘𝐷) & ⊢ 𝐽 = (Hom ‘𝐸) & ⊢ 1 = (Id‘𝐷) & ⊢ 𝐼 = (Id‘𝐸) & ⊢ · = (comp‘𝐷) & ⊢ 𝑂 = (comp‘𝐸) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝐸 ∈ Cat) ⇒ ⊢ (𝜑 → (𝐹(𝐷 Func 𝐸)𝐺 ↔ (𝐹:𝐵⟶𝐶 ∧ 𝐺 ∈ X𝑧 ∈ (𝐵 × 𝐵)(((𝐹‘(1st ‘𝑧))𝐽(𝐹‘(2nd ‘𝑧))) ↑m (𝐻‘𝑧)) ∧ ∀𝑥 ∈ 𝐵 (((𝑥𝐺𝑥)‘( 1 ‘𝑥)) = (𝐼‘(𝐹‘𝑥)) ∧ ∀𝑦 ∈ 𝐵 ∀𝑧 ∈ 𝐵 ∀𝑚 ∈ (𝑥𝐻𝑦)∀𝑛 ∈ (𝑦𝐻𝑧)((𝑥𝐺𝑧)‘(𝑛(〈𝑥, 𝑦〉 · 𝑧)𝑚)) = (((𝑦𝐺𝑧)‘𝑛)(〈(𝐹‘𝑥), (𝐹‘𝑦)〉𝑂(𝐹‘𝑧))((𝑥𝐺𝑦)‘𝑚)))))) | ||
| Theorem | isfuncd 17910* | Deduce that an operation is a functor of categories. (Contributed by Mario Carneiro, 4-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐶 = (Base‘𝐸) & ⊢ 𝐻 = (Hom ‘𝐷) & ⊢ 𝐽 = (Hom ‘𝐸) & ⊢ 1 = (Id‘𝐷) & ⊢ 𝐼 = (Id‘𝐸) & ⊢ · = (comp‘𝐷) & ⊢ 𝑂 = (comp‘𝐸) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝐸 ∈ Cat) & ⊢ (𝜑 → 𝐹:𝐵⟶𝐶) & ⊢ (𝜑 → 𝐺 Fn (𝐵 × 𝐵)) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵)) → (𝑥𝐺𝑦):(𝑥𝐻𝑦)⟶((𝐹‘𝑥)𝐽(𝐹‘𝑦))) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ((𝑥𝐺𝑥)‘( 1 ‘𝑥)) = (𝐼‘(𝐹‘𝑥))) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐵) ∧ (𝑚 ∈ (𝑥𝐻𝑦) ∧ 𝑛 ∈ (𝑦𝐻𝑧))) → ((𝑥𝐺𝑧)‘(𝑛(〈𝑥, 𝑦〉 · 𝑧)𝑚)) = (((𝑦𝐺𝑧)‘𝑛)(〈(𝐹‘𝑥), (𝐹‘𝑦)〉𝑂(𝐹‘𝑧))((𝑥𝐺𝑦)‘𝑚))) ⇒ ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) | ||
| Theorem | funcf1 17911 | The object part of a functor is a function on objects. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐶 = (Base‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) ⇒ ⊢ (𝜑 → 𝐹:𝐵⟶𝐶) | ||
| Theorem | funcixp 17912* | The morphism part of a functor is a function on homsets. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐷) & ⊢ 𝐽 = (Hom ‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) ⇒ ⊢ (𝜑 → 𝐺 ∈ X𝑧 ∈ (𝐵 × 𝐵)(((𝐹‘(1st ‘𝑧))𝐽(𝐹‘(2nd ‘𝑧))) ↑m (𝐻‘𝑧))) | ||
| Theorem | funcf2 17913 | The morphism part of a functor is a function on homsets. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐷) & ⊢ 𝐽 = (Hom ‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋𝐺𝑌):(𝑋𝐻𝑌)⟶((𝐹‘𝑋)𝐽(𝐹‘𝑌))) | ||
| Theorem | funcfn2 17914 | The morphism part of a functor is a function. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) ⇒ ⊢ (𝜑 → 𝐺 Fn (𝐵 × 𝐵)) | ||
| Theorem | funcid 17915 | A functor maps each identity to the corresponding identity in the target category. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 1 = (Id‘𝐷) & ⊢ 𝐼 = (Id‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) ⇒ ⊢ (𝜑 → ((𝑋𝐺𝑋)‘( 1 ‘𝑋)) = (𝐼‘(𝐹‘𝑋))) | ||
| Theorem | funcco 17916 | A functor maps composition in the source category to composition in the target. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐷) & ⊢ · = (comp‘𝐷) & ⊢ 𝑂 = (comp‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑍 ∈ 𝐵) & ⊢ (𝜑 → 𝑀 ∈ (𝑋𝐻𝑌)) & ⊢ (𝜑 → 𝑁 ∈ (𝑌𝐻𝑍)) ⇒ ⊢ (𝜑 → ((𝑋𝐺𝑍)‘(𝑁(〈𝑋, 𝑌〉 · 𝑍)𝑀)) = (((𝑌𝐺𝑍)‘𝑁)(〈(𝐹‘𝑋), (𝐹‘𝑌)〉𝑂(𝐹‘𝑍))((𝑋𝐺𝑌)‘𝑀))) | ||
| Theorem | funcsect 17917 | The image of a section under a functor is a section. (Contributed by Mario Carneiro, 2-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝑆 = (Sect‘𝐷) & ⊢ 𝑇 = (Sect‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑀(𝑋𝑆𝑌)𝑁) ⇒ ⊢ (𝜑 → ((𝑋𝐺𝑌)‘𝑀)((𝐹‘𝑋)𝑇(𝐹‘𝑌))((𝑌𝐺𝑋)‘𝑁)) | ||
| Theorem | funcinv 17918 | The image of an inverse under a functor is an inverse. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐼 = (Inv‘𝐷) & ⊢ 𝐽 = (Inv‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑀(𝑋𝐼𝑌)𝑁) ⇒ ⊢ (𝜑 → ((𝑋𝐺𝑌)‘𝑀)((𝐹‘𝑋)𝐽(𝐹‘𝑌))((𝑌𝐺𝑋)‘𝑁)) | ||
| Theorem | funciso 17919 | The image of an isomorphism under a functor is an isomorphism. Proposition 3.21 of [Adamek] p. 32. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐷) & ⊢ 𝐼 = (Iso‘𝐷) & ⊢ 𝐽 = (Iso‘𝐸) & ⊢ (𝜑 → 𝐹(𝐷 Func 𝐸)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑀 ∈ (𝑋𝐼𝑌)) ⇒ ⊢ (𝜑 → ((𝑋𝐺𝑌)‘𝑀) ∈ ((𝐹‘𝑋)𝐽(𝐹‘𝑌))) | ||
| Theorem | funcoppc 17920 | A functor on categories yields a functor on the opposite categories (in the same direction), see definition 3.41 of [Adamek] p. 39. (Contributed by Mario Carneiro, 4-Jan-2017.) |
| ⊢ 𝑂 = (oppCat‘𝐶) & ⊢ 𝑃 = (oppCat‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Func 𝐷)𝐺) ⇒ ⊢ (𝜑 → 𝐹(𝑂 Func 𝑃)tpos 𝐺) | ||
| Theorem | idfuval 17921* | Value of the identity functor. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐶 ∈ Cat) & ⊢ 𝐻 = (Hom ‘𝐶) ⇒ ⊢ (𝜑 → 𝐼 = 〈( I ↾ 𝐵), (𝑧 ∈ (𝐵 × 𝐵) ↦ ( I ↾ (𝐻‘𝑧)))〉) | ||
| Theorem | idfu2nd 17922 | Value of the morphism part of the identity functor. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐶 ∈ Cat) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋(2nd ‘𝐼)𝑌) = ( I ↾ (𝑋𝐻𝑌))) | ||
| Theorem | idfu2 17923 | Value of the morphism part of the identity functor. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐶 ∈ Cat) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝐹 ∈ (𝑋𝐻𝑌)) ⇒ ⊢ (𝜑 → ((𝑋(2nd ‘𝐼)𝑌)‘𝐹) = 𝐹) | ||
| Theorem | idfu1st 17924 | Value of the object part of the identity functor. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐶 ∈ Cat) ⇒ ⊢ (𝜑 → (1st ‘𝐼) = ( I ↾ 𝐵)) | ||
| Theorem | idfu1 17925 | Value of the object part of the identity functor. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐶 ∈ Cat) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) ⇒ ⊢ (𝜑 → ((1st ‘𝐼)‘𝑋) = 𝑋) | ||
| Theorem | idfucl 17926 | The identity functor is a functor. Example 3.20(1) of [Adamek] p. 30. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) ⇒ ⊢ (𝐶 ∈ Cat → 𝐼 ∈ (𝐶 Func 𝐶)) | ||
| Theorem | cofuval 17927* | Value of the composition of two functors. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) ⇒ ⊢ (𝜑 → (𝐺 ∘func 𝐹) = 〈((1st ‘𝐺) ∘ (1st ‘𝐹)), (𝑥 ∈ 𝐵, 𝑦 ∈ 𝐵 ↦ ((((1st ‘𝐹)‘𝑥)(2nd ‘𝐺)((1st ‘𝐹)‘𝑦)) ∘ (𝑥(2nd ‘𝐹)𝑦)))〉) | ||
| Theorem | cofu1st 17928 | Value of the object part of the functor composition. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) ⇒ ⊢ (𝜑 → (1st ‘(𝐺 ∘func 𝐹)) = ((1st ‘𝐺) ∘ (1st ‘𝐹))) | ||
| Theorem | cofu1 17929 | Value of the object part of the functor composition. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) ⇒ ⊢ (𝜑 → ((1st ‘(𝐺 ∘func 𝐹))‘𝑋) = ((1st ‘𝐺)‘((1st ‘𝐹)‘𝑋))) | ||
| Theorem | cofu2nd 17930 | Value of the morphism part of the functor composition. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋(2nd ‘(𝐺 ∘func 𝐹))𝑌) = ((((1st ‘𝐹)‘𝑋)(2nd ‘𝐺)((1st ‘𝐹)‘𝑌)) ∘ (𝑋(2nd ‘𝐹)𝑌))) | ||
| Theorem | cofu2 17931 | Value of the morphism part of the functor composition. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐻𝑌)) ⇒ ⊢ (𝜑 → ((𝑋(2nd ‘(𝐺 ∘func 𝐹))𝑌)‘𝑅) = ((((1st ‘𝐹)‘𝑋)(2nd ‘𝐺)((1st ‘𝐹)‘𝑌))‘((𝑋(2nd ‘𝐹)𝑌)‘𝑅))) | ||
| Theorem | cofuval2 17932* | Value of the composition of two functors. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Func 𝐷)𝐺) & ⊢ (𝜑 → 𝐻(𝐷 Func 𝐸)𝐾) ⇒ ⊢ (𝜑 → (〈𝐻, 𝐾〉 ∘func 〈𝐹, 𝐺〉) = 〈(𝐻 ∘ 𝐹), (𝑥 ∈ 𝐵, 𝑦 ∈ 𝐵 ↦ (((𝐹‘𝑥)𝐾(𝐹‘𝑦)) ∘ (𝑥𝐺𝑦)))〉) | ||
| Theorem | cofucl 17933 | The composition of two functors is a functor. Proposition 3.23 of [Adamek] p. 33. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Func 𝐸)) ⇒ ⊢ (𝜑 → (𝐺 ∘func 𝐹) ∈ (𝐶 Func 𝐸)) | ||
| Theorem | cofuass 17934 | Functor composition is associative. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ (𝜑 → 𝐺 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐻 ∈ (𝐷 Func 𝐸)) & ⊢ (𝜑 → 𝐾 ∈ (𝐸 Func 𝐹)) ⇒ ⊢ (𝜑 → ((𝐾 ∘func 𝐻) ∘func 𝐺) = (𝐾 ∘func (𝐻 ∘func 𝐺))) | ||
| Theorem | cofulid 17935 | The identity functor is a left identity for composition. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ 𝐼 = (idfunc‘𝐷) ⇒ ⊢ (𝜑 → (𝐼 ∘func 𝐹) = 𝐹) | ||
| Theorem | cofurid 17936 | The identity functor is a right identity for composition. (Contributed by Mario Carneiro, 3-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ 𝐼 = (idfunc‘𝐶) ⇒ ⊢ (𝜑 → (𝐹 ∘func 𝐼) = 𝐹) | ||
| Theorem | resfval 17937* | Value of the functor restriction operator. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ 𝑉) & ⊢ (𝜑 → 𝐻 ∈ 𝑊) ⇒ ⊢ (𝜑 → (𝐹 ↾f 𝐻) = 〈((1st ‘𝐹) ↾ dom dom 𝐻), (𝑥 ∈ dom 𝐻 ↦ (((2nd ‘𝐹)‘𝑥) ↾ (𝐻‘𝑥)))〉) | ||
| Theorem | resfval2 17938* | Value of the functor restriction operator. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ 𝑉) & ⊢ (𝜑 → 𝐻 ∈ 𝑊) & ⊢ (𝜑 → 𝐺 ∈ 𝑋) & ⊢ (𝜑 → 𝐻 Fn (𝑆 × 𝑆)) ⇒ ⊢ (𝜑 → (〈𝐹, 𝐺〉 ↾f 𝐻) = 〈(𝐹 ↾ 𝑆), (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ ((𝑥𝐺𝑦) ↾ (𝑥𝐻𝑦)))〉) | ||
| Theorem | resf1st 17939 | Value of the functor restriction operator on objects. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ 𝑉) & ⊢ (𝜑 → 𝐻 ∈ 𝑊) & ⊢ (𝜑 → 𝐻 Fn (𝑆 × 𝑆)) ⇒ ⊢ (𝜑 → (1st ‘(𝐹 ↾f 𝐻)) = ((1st ‘𝐹) ↾ 𝑆)) | ||
| Theorem | resf2nd 17940 | Value of the functor restriction operator on morphisms. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ 𝑉) & ⊢ (𝜑 → 𝐻 ∈ 𝑊) & ⊢ (𝜑 → 𝐻 Fn (𝑆 × 𝑆)) & ⊢ (𝜑 → 𝑋 ∈ 𝑆) & ⊢ (𝜑 → 𝑌 ∈ 𝑆) ⇒ ⊢ (𝜑 → (𝑋(2nd ‘(𝐹 ↾f 𝐻))𝑌) = ((𝑋(2nd ‘𝐹)𝑌) ↾ (𝑋𝐻𝑌))) | ||
| Theorem | funcres 17941 | A functor restricted to a subcategory is a functor. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐻 ∈ (Subcat‘𝐶)) ⇒ ⊢ (𝜑 → (𝐹 ↾f 𝐻) ∈ ((𝐶 ↾cat 𝐻) Func 𝐷)) | ||
| Theorem | funcres2b 17942* | Condition for a functor to also be a functor into the restriction. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝑅 ∈ (Subcat‘𝐷)) & ⊢ (𝜑 → 𝑅 Fn (𝑆 × 𝑆)) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐴 ∧ 𝑦 ∈ 𝐴)) → (𝑥𝐺𝑦):𝑌⟶((𝐹‘𝑥)𝑅(𝐹‘𝑦))) ⇒ ⊢ (𝜑 → (𝐹(𝐶 Func 𝐷)𝐺 ↔ 𝐹(𝐶 Func (𝐷 ↾cat 𝑅))𝐺)) | ||
| Theorem | funcres2 17943 | A functor into a restricted category is also a functor into the whole category. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ (𝑅 ∈ (Subcat‘𝐷) → (𝐶 Func (𝐷 ↾cat 𝑅)) ⊆ (𝐶 Func 𝐷)) | ||
| Theorem | idfusubc0 17944* | The identity functor for a subcategory is an "inclusion functor" from the subcategory into its supercategory. (Contributed by AV, 29-Mar-2020.) |
| ⊢ 𝑆 = (𝐶 ↾cat 𝐽) & ⊢ 𝐼 = (idfunc‘𝑆) & ⊢ 𝐵 = (Base‘𝑆) ⇒ ⊢ (𝐽 ∈ (Subcat‘𝐶) → 𝐼 = 〈( I ↾ 𝐵), (𝑥 ∈ 𝐵, 𝑦 ∈ 𝐵 ↦ ( I ↾ (𝑥(Hom ‘𝑆)𝑦)))〉) | ||
| Theorem | idfusubc 17945* | The identity functor for a subcategory is an "inclusion functor" from the subcategory into its supercategory. (Contributed by AV, 29-Mar-2020.) |
| ⊢ 𝑆 = (𝐶 ↾cat 𝐽) & ⊢ 𝐼 = (idfunc‘𝑆) & ⊢ 𝐵 = (Base‘𝑆) ⇒ ⊢ (𝐽 ∈ (Subcat‘𝐶) → 𝐼 = 〈( I ↾ 𝐵), (𝑥 ∈ 𝐵, 𝑦 ∈ 𝐵 ↦ ( I ↾ (𝑥𝐽𝑦)))〉) | ||
| Theorem | wunfunc 17946 | A weak universe is closed under the functor set operation. (Contributed by Mario Carneiro, 12-Jan-2017.) (Proof shortened by AV, 13-Oct-2024.) |
| ⊢ (𝜑 → 𝑈 ∈ WUni) & ⊢ (𝜑 → 𝐶 ∈ 𝑈) & ⊢ (𝜑 → 𝐷 ∈ 𝑈) ⇒ ⊢ (𝜑 → (𝐶 Func 𝐷) ∈ 𝑈) | ||
| Theorem | funcpropd 17947 | If two categories have the same set of objects, morphisms, and compositions, then they have the same functors. (Contributed by Mario Carneiro, 17-Jan-2017.) |
| ⊢ (𝜑 → (Homf ‘𝐴) = (Homf ‘𝐵)) & ⊢ (𝜑 → (compf‘𝐴) = (compf‘𝐵)) & ⊢ (𝜑 → (Homf ‘𝐶) = (Homf ‘𝐷)) & ⊢ (𝜑 → (compf‘𝐶) = (compf‘𝐷)) & ⊢ (𝜑 → 𝐴 ∈ 𝑉) & ⊢ (𝜑 → 𝐵 ∈ 𝑉) & ⊢ (𝜑 → 𝐶 ∈ 𝑉) & ⊢ (𝜑 → 𝐷 ∈ 𝑉) ⇒ ⊢ (𝜑 → (𝐴 Func 𝐶) = (𝐵 Func 𝐷)) | ||
| Theorem | funcres2c 17948 | Condition for a functor to also be a functor into the restriction. (Contributed by Mario Carneiro, 30-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐸 = (𝐷 ↾s 𝑆) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝑆 ∈ 𝑉) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) ⇒ ⊢ (𝜑 → (𝐹(𝐶 Func 𝐷)𝐺 ↔ 𝐹(𝐶 Func 𝐸)𝐺)) | ||
| Syntax | cful 17949 | Extend class notation with the class of all full functors. |
| class Full | ||
| Syntax | cfth 17950 | Extend class notation with the class of all faithful functors. |
| class Faith | ||
| Definition | df-full 17951* | Function returning all the full functors from a category 𝐶 to a category 𝐷. A full functor is a functor in which all the morphism maps 𝐺(𝑋, 𝑌) between objects 𝑋, 𝑌 ∈ 𝐶 are surjections. Definition 3.27(3) in [Adamek] p. 34. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ Full = (𝑐 ∈ Cat, 𝑑 ∈ Cat ↦ {〈𝑓, 𝑔〉 ∣ (𝑓(𝑐 Func 𝑑)𝑔 ∧ ∀𝑥 ∈ (Base‘𝑐)∀𝑦 ∈ (Base‘𝑐)ran (𝑥𝑔𝑦) = ((𝑓‘𝑥)(Hom ‘𝑑)(𝑓‘𝑦)))}) | ||
| Definition | df-fth 17952* | Function returning all the faithful functors from a category 𝐶 to a category 𝐷. A faithful functor is a functor in which all the morphism maps 𝐺(𝑋, 𝑌) between objects 𝑋, 𝑌 ∈ 𝐶 are injections. Definition 3.27(2) in [Adamek] p. 34. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ Faith = (𝑐 ∈ Cat, 𝑑 ∈ Cat ↦ {〈𝑓, 𝑔〉 ∣ (𝑓(𝑐 Func 𝑑)𝑔 ∧ ∀𝑥 ∈ (Base‘𝑐)∀𝑦 ∈ (Base‘𝑐)Fun ◡(𝑥𝑔𝑦))}) | ||
| Theorem | fullfunc 17953 | A full functor is a functor. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ (𝐶 Full 𝐷) ⊆ (𝐶 Func 𝐷) | ||
| Theorem | fthfunc 17954 | A faithful functor is a functor. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ (𝐶 Faith 𝐷) ⊆ (𝐶 Func 𝐷) | ||
| Theorem | relfull 17955 | The set of full functors is a relation. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ Rel (𝐶 Full 𝐷) | ||
| Theorem | relfth 17956 | The set of faithful functors is a relation. (Contributed by Mario Carneiro, 26-Jan-2017.) |
| ⊢ Rel (𝐶 Faith 𝐷) | ||
| Theorem | isfull 17957* | Value of the set of full functors between two categories. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) ⇒ ⊢ (𝐹(𝐶 Full 𝐷)𝐺 ↔ (𝐹(𝐶 Func 𝐷)𝐺 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ran (𝑥𝐺𝑦) = ((𝐹‘𝑥)𝐽(𝐹‘𝑦)))) | ||
| Theorem | isfull2 17958* | Equivalent condition for a full functor. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐶) ⇒ ⊢ (𝐹(𝐶 Full 𝐷)𝐺 ↔ (𝐹(𝐶 Func 𝐷)𝐺 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 (𝑥𝐺𝑦):(𝑥𝐻𝑦)–onto→((𝐹‘𝑥)𝐽(𝐹‘𝑦)))) | ||
| Theorem | fullfo 17959 | The morphism map of a full functor is a surjection. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Full 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋𝐺𝑌):(𝑋𝐻𝑌)–onto→((𝐹‘𝑋)𝐽(𝐹‘𝑌))) | ||
| Theorem | fulli 17960* | The morphism map of a full functor is a surjection. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Full 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑅 ∈ ((𝐹‘𝑋)𝐽(𝐹‘𝑌))) ⇒ ⊢ (𝜑 → ∃𝑓 ∈ (𝑋𝐻𝑌)𝑅 = ((𝑋𝐺𝑌)‘𝑓)) | ||
| Theorem | isfth 17961* | Value of the set of faithful functors between two categories. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) ⇒ ⊢ (𝐹(𝐶 Faith 𝐷)𝐺 ↔ (𝐹(𝐶 Func 𝐷)𝐺 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 Fun ◡(𝑥𝐺𝑦))) | ||
| Theorem | isfth2 17962* | Equivalent condition for a faithful functor. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) ⇒ ⊢ (𝐹(𝐶 Faith 𝐷)𝐺 ↔ (𝐹(𝐶 Func 𝐷)𝐺 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 (𝑥𝐺𝑦):(𝑥𝐻𝑦)–1-1→((𝐹‘𝑥)𝐽(𝐹‘𝑦)))) | ||
| Theorem | isffth2 17963* | A fully faithful functor is a functor which is bijective on hom-sets. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) ⇒ ⊢ (𝐹((𝐶 Full 𝐷) ∩ (𝐶 Faith 𝐷))𝐺 ↔ (𝐹(𝐶 Func 𝐷)𝐺 ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 (𝑥𝐺𝑦):(𝑥𝐻𝑦)–1-1-onto→((𝐹‘𝑥)𝐽(𝐹‘𝑦)))) | ||
| Theorem | fthf1 17964 | The morphism map of a faithful functor is an injection. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋𝐺𝑌):(𝑋𝐻𝑌)–1-1→((𝐹‘𝑋)𝐽(𝐹‘𝑌))) | ||
| Theorem | fthi 17965 | The morphism map of a faithful functor is an injection. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐻𝑌)) & ⊢ (𝜑 → 𝑆 ∈ (𝑋𝐻𝑌)) ⇒ ⊢ (𝜑 → (((𝑋𝐺𝑌)‘𝑅) = ((𝑋𝐺𝑌)‘𝑆) ↔ 𝑅 = 𝑆)) | ||
| Theorem | ffthf1o 17966 | The morphism map of a fully faithful functor is a bijection. (Contributed by Mario Carneiro, 29-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ (𝜑 → 𝐹((𝐶 Full 𝐷) ∩ (𝐶 Faith 𝐷))𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋𝐺𝑌):(𝑋𝐻𝑌)–1-1-onto→((𝐹‘𝑋)𝐽(𝐹‘𝑌))) | ||
| Theorem | fullpropd 17967 | If two categories have the same set of objects, morphisms, and compositions, then they have the same full functors. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ (𝜑 → (Homf ‘𝐴) = (Homf ‘𝐵)) & ⊢ (𝜑 → (compf‘𝐴) = (compf‘𝐵)) & ⊢ (𝜑 → (Homf ‘𝐶) = (Homf ‘𝐷)) & ⊢ (𝜑 → (compf‘𝐶) = (compf‘𝐷)) & ⊢ (𝜑 → 𝐴 ∈ 𝑉) & ⊢ (𝜑 → 𝐵 ∈ 𝑉) & ⊢ (𝜑 → 𝐶 ∈ 𝑉) & ⊢ (𝜑 → 𝐷 ∈ 𝑉) ⇒ ⊢ (𝜑 → (𝐴 Full 𝐶) = (𝐵 Full 𝐷)) | ||
| Theorem | fthpropd 17968 | If two categories have the same set of objects, morphisms, and compositions, then they have the same faithful functors. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ (𝜑 → (Homf ‘𝐴) = (Homf ‘𝐵)) & ⊢ (𝜑 → (compf‘𝐴) = (compf‘𝐵)) & ⊢ (𝜑 → (Homf ‘𝐶) = (Homf ‘𝐷)) & ⊢ (𝜑 → (compf‘𝐶) = (compf‘𝐷)) & ⊢ (𝜑 → 𝐴 ∈ 𝑉) & ⊢ (𝜑 → 𝐵 ∈ 𝑉) & ⊢ (𝜑 → 𝐶 ∈ 𝑉) & ⊢ (𝜑 → 𝐷 ∈ 𝑉) ⇒ ⊢ (𝜑 → (𝐴 Faith 𝐶) = (𝐵 Faith 𝐷)) | ||
| Theorem | fulloppc 17969 | The opposite functor of a full functor is also full. Proposition 3.43(d) in [Adamek] p. 39. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝑂 = (oppCat‘𝐶) & ⊢ 𝑃 = (oppCat‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Full 𝐷)𝐺) ⇒ ⊢ (𝜑 → 𝐹(𝑂 Full 𝑃)tpos 𝐺) | ||
| Theorem | fthoppc 17970 | The opposite functor of a faithful functor is also faithful. Proposition 3.43(c) in [Adamek] p. 39. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝑂 = (oppCat‘𝐶) & ⊢ 𝑃 = (oppCat‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) ⇒ ⊢ (𝜑 → 𝐹(𝑂 Faith 𝑃)tpos 𝐺) | ||
| Theorem | ffthoppc 17971 | The opposite functor of a fully faithful functor is also full and faithful. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝑂 = (oppCat‘𝐶) & ⊢ 𝑃 = (oppCat‘𝐷) & ⊢ (𝜑 → 𝐹((𝐶 Full 𝐷) ∩ (𝐶 Faith 𝐷))𝐺) ⇒ ⊢ (𝜑 → 𝐹((𝑂 Full 𝑃) ∩ (𝑂 Faith 𝑃))tpos 𝐺) | ||
| Theorem | fthsect 17972 | A faithful functor reflects sections. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑀 ∈ (𝑋𝐻𝑌)) & ⊢ (𝜑 → 𝑁 ∈ (𝑌𝐻𝑋)) & ⊢ 𝑆 = (Sect‘𝐶) & ⊢ 𝑇 = (Sect‘𝐷) ⇒ ⊢ (𝜑 → (𝑀(𝑋𝑆𝑌)𝑁 ↔ ((𝑋𝐺𝑌)‘𝑀)((𝐹‘𝑋)𝑇(𝐹‘𝑌))((𝑌𝐺𝑋)‘𝑁))) | ||
| Theorem | fthinv 17973 | A faithful functor reflects inverses. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑀 ∈ (𝑋𝐻𝑌)) & ⊢ (𝜑 → 𝑁 ∈ (𝑌𝐻𝑋)) & ⊢ 𝐼 = (Inv‘𝐶) & ⊢ 𝐽 = (Inv‘𝐷) ⇒ ⊢ (𝜑 → (𝑀(𝑋𝐼𝑌)𝑁 ↔ ((𝑋𝐺𝑌)‘𝑀)((𝐹‘𝑋)𝐽(𝐹‘𝑌))((𝑌𝐺𝑋)‘𝑁))) | ||
| Theorem | fthmon 17974 | A faithful functor reflects monomorphisms. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐻𝑌)) & ⊢ 𝑀 = (Mono‘𝐶) & ⊢ 𝑁 = (Mono‘𝐷) & ⊢ (𝜑 → ((𝑋𝐺𝑌)‘𝑅) ∈ ((𝐹‘𝑋)𝑁(𝐹‘𝑌))) ⇒ ⊢ (𝜑 → 𝑅 ∈ (𝑋𝑀𝑌)) | ||
| Theorem | fthepi 17975 | A faithful functor reflects epimorphisms. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐻𝑌)) & ⊢ 𝐸 = (Epi‘𝐶) & ⊢ 𝑃 = (Epi‘𝐷) & ⊢ (𝜑 → ((𝑋𝐺𝑌)‘𝑅) ∈ ((𝐹‘𝑋)𝑃(𝐹‘𝑌))) ⇒ ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐸𝑌)) | ||
| Theorem | ffthiso 17976 | A fully faithful functor reflects isomorphisms. Corollary 3.32 of [Adamek] p. 35. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝐹(𝐶 Faith 𝐷)𝐺) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑅 ∈ (𝑋𝐻𝑌)) & ⊢ (𝜑 → 𝐹(𝐶 Full 𝐷)𝐺) & ⊢ 𝐼 = (Iso‘𝐶) & ⊢ 𝐽 = (Iso‘𝐷) ⇒ ⊢ (𝜑 → (𝑅 ∈ (𝑋𝐼𝑌) ↔ ((𝑋𝐺𝑌)‘𝑅) ∈ ((𝐹‘𝑋)𝐽(𝐹‘𝑌)))) | ||
| Theorem | fthres2b 17977* | Condition for a faithful functor to also be a faithful functor into the restriction. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ (𝜑 → 𝑅 ∈ (Subcat‘𝐷)) & ⊢ (𝜑 → 𝑅 Fn (𝑆 × 𝑆)) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐴 ∧ 𝑦 ∈ 𝐴)) → (𝑥𝐺𝑦):𝑌⟶((𝐹‘𝑥)𝑅(𝐹‘𝑦))) ⇒ ⊢ (𝜑 → (𝐹(𝐶 Faith 𝐷)𝐺 ↔ 𝐹(𝐶 Faith (𝐷 ↾cat 𝑅))𝐺)) | ||
| Theorem | fthres2c 17978 | Condition for a faithful functor to also be a faithful functor into the restriction. (Contributed by Mario Carneiro, 30-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐸 = (𝐷 ↾s 𝑆) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝑆 ∈ 𝑉) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) ⇒ ⊢ (𝜑 → (𝐹(𝐶 Faith 𝐷)𝐺 ↔ 𝐹(𝐶 Faith 𝐸)𝐺)) | ||
| Theorem | fthres2 17979 | A faithful functor into a restricted category is also a faithful functor into the whole category. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ (𝑅 ∈ (Subcat‘𝐷) → (𝐶 Faith (𝐷 ↾cat 𝑅)) ⊆ (𝐶 Faith 𝐷)) | ||
| Theorem | idffth 17980 | The identity functor is a fully faithful functor. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐼 = (idfunc‘𝐶) ⇒ ⊢ (𝐶 ∈ Cat → 𝐼 ∈ ((𝐶 Full 𝐶) ∩ (𝐶 Faith 𝐶))) | ||
| Theorem | cofull 17981 | The composition of two full functors is full. Proposition 3.30(d) in [Adamek] p. 35. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Full 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Full 𝐸)) ⇒ ⊢ (𝜑 → (𝐺 ∘func 𝐹) ∈ (𝐶 Full 𝐸)) | ||
| Theorem | cofth 17982 | The composition of two faithful functors is faithful. Proposition 3.30(c) in [Adamek] p. 35. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ (𝐶 Faith 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐷 Faith 𝐸)) ⇒ ⊢ (𝜑 → (𝐺 ∘func 𝐹) ∈ (𝐶 Faith 𝐸)) | ||
| Theorem | coffth 17983 | The composition of two fully faithful functors is fully faithful. (Contributed by Mario Carneiro, 28-Jan-2017.) |
| ⊢ (𝜑 → 𝐹 ∈ ((𝐶 Full 𝐷) ∩ (𝐶 Faith 𝐷))) & ⊢ (𝜑 → 𝐺 ∈ ((𝐷 Full 𝐸) ∩ (𝐷 Faith 𝐸))) ⇒ ⊢ (𝜑 → (𝐺 ∘func 𝐹) ∈ ((𝐶 Full 𝐸) ∩ (𝐶 Faith 𝐸))) | ||
| Theorem | rescfth 17984 | The inclusion functor from a subcategory is a faithful functor. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐷 = (𝐶 ↾cat 𝐽) & ⊢ 𝐼 = (idfunc‘𝐷) ⇒ ⊢ (𝐽 ∈ (Subcat‘𝐶) → 𝐼 ∈ (𝐷 Faith 𝐶)) | ||
| Theorem | ressffth 17985 | The inclusion functor from a full subcategory is a full and faithful functor, see also remark 4.4(2) in [Adamek] p. 49. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐷 = (𝐶 ↾s 𝑆) & ⊢ 𝐼 = (idfunc‘𝐷) ⇒ ⊢ ((𝐶 ∈ Cat ∧ 𝑆 ∈ 𝑉) → 𝐼 ∈ ((𝐷 Full 𝐶) ∩ (𝐷 Faith 𝐶))) | ||
| Theorem | fullres2c 17986 | Condition for a full functor to also be a full functor into the restriction. (Contributed by Mario Carneiro, 30-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐸 = (𝐷 ↾s 𝑆) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝑆 ∈ 𝑉) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) ⇒ ⊢ (𝜑 → (𝐹(𝐶 Full 𝐷)𝐺 ↔ 𝐹(𝐶 Full 𝐸)𝐺)) | ||
| Theorem | ffthres2c 17987 | Condition for a fully faithful functor to also be a fully faithful functor into the restriction. (Contributed by Mario Carneiro, 27-Jan-2017.) |
| ⊢ 𝐴 = (Base‘𝐶) & ⊢ 𝐸 = (𝐷 ↾s 𝑆) & ⊢ (𝜑 → 𝐷 ∈ Cat) & ⊢ (𝜑 → 𝑆 ∈ 𝑉) & ⊢ (𝜑 → 𝐹:𝐴⟶𝑆) ⇒ ⊢ (𝜑 → (𝐹((𝐶 Full 𝐷) ∩ (𝐶 Faith 𝐷))𝐺 ↔ 𝐹((𝐶 Full 𝐸) ∩ (𝐶 Faith 𝐸))𝐺)) | ||
| Theorem | inclfusubc 17988* | The "inclusion functor" from a subcategory of a category into the category itself. (Contributed by AV, 30-Mar-2020.) |
| ⊢ (𝜑 → 𝐽 ∈ (Subcat‘𝐶)) & ⊢ 𝑆 = (𝐶 ↾cat 𝐽) & ⊢ 𝐵 = (Base‘𝑆) & ⊢ (𝜑 → 𝐹 = ( I ↾ 𝐵)) & ⊢ (𝜑 → 𝐺 = (𝑥 ∈ 𝐵, 𝑦 ∈ 𝐵 ↦ ( I ↾ (𝑥𝐽𝑦)))) ⇒ ⊢ (𝜑 → 𝐹(𝑆 Func 𝐶)𝐺) | ||
| Syntax | cnat 17989 | Extend class notation to include the collection of natural transformations. |
| class Nat | ||
| Syntax | cfuc 17990 | Extend class notation to include the functor category. |
| class FuncCat | ||
| Definition | df-nat 17991* | Definition of a natural transformation between two functors. A natural transformation 𝐴:𝐹⟶𝐺 is a collection of arrows 𝐴(𝑥):𝐹(𝑥)⟶𝐺(𝑥), such that 𝐴(𝑦) ∘ 𝐹(ℎ) = 𝐺(ℎ) ∘ 𝐴(𝑥) for each morphism ℎ:𝑥⟶𝑦. Definition 6.1 in [Adamek] p. 83, and definition in [Lang] p. 65. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ Nat = (𝑡 ∈ Cat, 𝑢 ∈ Cat ↦ (𝑓 ∈ (𝑡 Func 𝑢), 𝑔 ∈ (𝑡 Func 𝑢) ↦ ⦋(1st ‘𝑓) / 𝑟⦌⦋(1st ‘𝑔) / 𝑠⦌{𝑎 ∈ X𝑥 ∈ (Base‘𝑡)((𝑟‘𝑥)(Hom ‘𝑢)(𝑠‘𝑥)) ∣ ∀𝑥 ∈ (Base‘𝑡)∀𝑦 ∈ (Base‘𝑡)∀ℎ ∈ (𝑥(Hom ‘𝑡)𝑦)((𝑎‘𝑦)(〈(𝑟‘𝑥), (𝑟‘𝑦)〉(comp‘𝑢)(𝑠‘𝑦))((𝑥(2nd ‘𝑓)𝑦)‘ℎ)) = (((𝑥(2nd ‘𝑔)𝑦)‘ℎ)(〈(𝑟‘𝑥), (𝑠‘𝑥)〉(comp‘𝑢)(𝑠‘𝑦))(𝑎‘𝑥))})) | ||
| Definition | df-fuc 17992* | Definition of the category of functors between two fixed categories, with the objects being functors and the morphisms being natural transformations. Definition 6.15 in [Adamek] p. 87. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ FuncCat = (𝑡 ∈ Cat, 𝑢 ∈ Cat ↦ {〈(Base‘ndx), (𝑡 Func 𝑢)〉, 〈(Hom ‘ndx), (𝑡 Nat 𝑢)〉, 〈(comp‘ndx), (𝑣 ∈ ((𝑡 Func 𝑢) × (𝑡 Func 𝑢)), ℎ ∈ (𝑡 Func 𝑢) ↦ ⦋(1st ‘𝑣) / 𝑓⦌⦋(2nd ‘𝑣) / 𝑔⦌(𝑏 ∈ (𝑔(𝑡 Nat 𝑢)ℎ), 𝑎 ∈ (𝑓(𝑡 Nat 𝑢)𝑔) ↦ (𝑥 ∈ (Base‘𝑡) ↦ ((𝑏‘𝑥)(〈((1st ‘𝑓)‘𝑥), ((1st ‘𝑔)‘𝑥)〉(comp‘𝑢)((1st ‘ℎ)‘𝑥))(𝑎‘𝑥)))))〉}) | ||
| Theorem | fnfuc 17993 | The FuncCat operation is a well-defined function on categories. (Contributed by Mario Carneiro, 12-Jan-2017.) |
| ⊢ FuncCat Fn (Cat × Cat) | ||
| Theorem | natfval 17994* | Value of the function giving natural transformations between two categories. (Contributed by Mario Carneiro, 6-Jan-2017.) (Proof shortened by AV, 1-Mar-2024.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ · = (comp‘𝐷) ⇒ ⊢ 𝑁 = (𝑓 ∈ (𝐶 Func 𝐷), 𝑔 ∈ (𝐶 Func 𝐷) ↦ ⦋(1st ‘𝑓) / 𝑟⦌⦋(1st ‘𝑔) / 𝑠⦌{𝑎 ∈ X𝑥 ∈ 𝐵 ((𝑟‘𝑥)𝐽(𝑠‘𝑥)) ∣ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ∀ℎ ∈ (𝑥𝐻𝑦)((𝑎‘𝑦)(〈(𝑟‘𝑥), (𝑟‘𝑦)〉 · (𝑠‘𝑦))((𝑥(2nd ‘𝑓)𝑦)‘ℎ)) = (((𝑥(2nd ‘𝑔)𝑦)‘ℎ)(〈(𝑟‘𝑥), (𝑠‘𝑥)〉 · (𝑠‘𝑦))(𝑎‘𝑥))}) | ||
| Theorem | isnat 17995* | Property of being a natural transformation. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ · = (comp‘𝐷) & ⊢ (𝜑 → 𝐹(𝐶 Func 𝐷)𝐺) & ⊢ (𝜑 → 𝐾(𝐶 Func 𝐷)𝐿) ⇒ ⊢ (𝜑 → (𝐴 ∈ (〈𝐹, 𝐺〉𝑁〈𝐾, 𝐿〉) ↔ (𝐴 ∈ X𝑥 ∈ 𝐵 ((𝐹‘𝑥)𝐽(𝐾‘𝑥)) ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ∀ℎ ∈ (𝑥𝐻𝑦)((𝐴‘𝑦)(〈(𝐹‘𝑥), (𝐹‘𝑦)〉 · (𝐾‘𝑦))((𝑥𝐺𝑦)‘ℎ)) = (((𝑥𝐿𝑦)‘ℎ)(〈(𝐹‘𝑥), (𝐾‘𝑥)〉 · (𝐾‘𝑦))(𝐴‘𝑥))))) | ||
| Theorem | isnat2 17996* | Property of being a natural transformation. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐻 = (Hom ‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) & ⊢ · = (comp‘𝐷) & ⊢ (𝜑 → 𝐹 ∈ (𝐶 Func 𝐷)) & ⊢ (𝜑 → 𝐺 ∈ (𝐶 Func 𝐷)) ⇒ ⊢ (𝜑 → (𝐴 ∈ (𝐹𝑁𝐺) ↔ (𝐴 ∈ X𝑥 ∈ 𝐵 (((1st ‘𝐹)‘𝑥)𝐽((1st ‘𝐺)‘𝑥)) ∧ ∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ∀ℎ ∈ (𝑥𝐻𝑦)((𝐴‘𝑦)(〈((1st ‘𝐹)‘𝑥), ((1st ‘𝐹)‘𝑦)〉 · ((1st ‘𝐺)‘𝑦))((𝑥(2nd ‘𝐹)𝑦)‘ℎ)) = (((𝑥(2nd ‘𝐺)𝑦)‘ℎ)(〈((1st ‘𝐹)‘𝑥), ((1st ‘𝐺)‘𝑥)〉 · ((1st ‘𝐺)‘𝑦))(𝐴‘𝑥))))) | ||
| Theorem | natffn 17997 | The natural transformation set operation is a well-defined function. (Contributed by Mario Carneiro, 12-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) ⇒ ⊢ 𝑁 Fn ((𝐶 Func 𝐷) × (𝐶 Func 𝐷)) | ||
| Theorem | natrcl 17998 | Reverse closure for a natural transformation. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) ⇒ ⊢ (𝐴 ∈ (𝐹𝑁𝐺) → (𝐹 ∈ (𝐶 Func 𝐷) ∧ 𝐺 ∈ (𝐶 Func 𝐷))) | ||
| Theorem | nat1st2nd 17999 | Rewrite the natural transformation predicate with separated functor parts. (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) & ⊢ (𝜑 → 𝐴 ∈ (𝐹𝑁𝐺)) ⇒ ⊢ (𝜑 → 𝐴 ∈ (〈(1st ‘𝐹), (2nd ‘𝐹)〉𝑁〈(1st ‘𝐺), (2nd ‘𝐺)〉)) | ||
| Theorem | natixp 18000* | A natural transformation is a function from the objects of 𝐶 to homomorphisms from 𝐹(𝑥) to 𝐺(𝑥). (Contributed by Mario Carneiro, 6-Jan-2017.) |
| ⊢ 𝑁 = (𝐶 Nat 𝐷) & ⊢ (𝜑 → 𝐴 ∈ (〈𝐹, 𝐺〉𝑁〈𝐾, 𝐿〉)) & ⊢ 𝐵 = (Base‘𝐶) & ⊢ 𝐽 = (Hom ‘𝐷) ⇒ ⊢ (𝜑 → 𝐴 ∈ X𝑥 ∈ 𝐵 ((𝐹‘𝑥)𝐽(𝐾‘𝑥))) | ||
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