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Theorem List for Metamath Proof Explorer - 49501-49600   *Has distinct variable group(s)
TypeLabelDescription
Statement
 
21.49.15.13  Product of categories
 
Theoremreldmxpc 49501 The binary product of categories is a proper operator, so it can be used with ovprc1 7397, elbasov 17143, strov2rcl 17144, and so on. See reldmxpcALT 49502 for an alternate proof with less "essential steps" but more "bytes". (Proposed by SN, 15-Oct-2025.) (Contributed by Zhi Wang, 15-Oct-2025.)
Rel dom ×c
 
TheoremreldmxpcALT 49502 Alternate proof of reldmxpc 49501. (Contributed by Zhi Wang, 15-Oct-2025.) (Proof modification is discouraged.) (New usage is discouraged.)
Rel dom ×c
 
Theoremelxpcbasex1 49503 A non-empty base set of the product category indicates the existence of the first factor of the product category. (Contributed by Zhi Wang, 8-Oct-2025.) (Proof shortened by SN, 15-Oct-2025.)
𝑇 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑇)    &   (𝜑𝑋𝐵)       (𝜑𝐶 ∈ V)
 
Theoremelxpcbasex1ALT 49504 Alternate proof of elxpcbasex1 49503. (Contributed by Zhi Wang, 8-Oct-2025.) (Proof modification is discouraged.) (New usage is discouraged.)
𝑇 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑇)    &   (𝜑𝑋𝐵)       (𝜑𝐶 ∈ V)
 
Theoremelxpcbasex2 49505 A non-empty base set of the product category indicates the existence of the second factor of the product category. (Contributed by Zhi Wang, 8-Oct-2025.) (Proof shortened by SN, 15-Oct-2025.)
𝑇 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑇)    &   (𝜑𝑋𝐵)       (𝜑𝐷 ∈ V)
 
Theoremelxpcbasex2ALT 49506 Alternate proof of elxpcbasex2 49505. (Contributed by Zhi Wang, 8-Oct-2025.) (Proof modification is discouraged.) (New usage is discouraged.)
𝑇 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑇)    &   (𝜑𝑋𝐵)       (𝜑𝐷 ∈ V)
 
Theoremxpcfucbas 49507 The base set of the product of two categories of functors. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))       ((𝐵 Func 𝐶) × (𝐷 Func 𝐸)) = (Base‘𝑇)
 
Theoremxpcfuchomfval 49508* Set of morphisms of the binary product of categories of functors. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   𝐴 = (Base‘𝑇)    &   𝐾 = (Hom ‘𝑇)       𝐾 = (𝑢𝐴, 𝑣𝐴 ↦ (((1st𝑢)(𝐵 Nat 𝐶)(1st𝑣)) × ((2nd𝑢)(𝐷 Nat 𝐸)(2nd𝑣))))
 
Theoremxpcfuchom 49509 Set of morphisms of the binary product of categories of functors. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   𝐴 = (Base‘𝑇)    &   𝐾 = (Hom ‘𝑇)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)       (𝜑 → (𝑋𝐾𝑌) = (((1st𝑋)(𝐵 Nat 𝐶)(1st𝑌)) × ((2nd𝑋)(𝐷 Nat 𝐸)(2nd𝑌))))
 
Theoremxpcfuchom2 49510 Value of the set of morphisms in the binary product of categories of functors. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   (𝜑𝑀 ∈ (𝐵 Func 𝐶))    &   (𝜑𝑁 ∈ (𝐷 Func 𝐸))    &   (𝜑𝑃 ∈ (𝐵 Func 𝐶))    &   (𝜑𝑄 ∈ (𝐷 Func 𝐸))    &   𝐾 = (Hom ‘𝑇)       (𝜑 → (⟨𝑀, 𝑁𝐾𝑃, 𝑄⟩) = ((𝑀(𝐵 Nat 𝐶)𝑃) × (𝑁(𝐷 Nat 𝐸)𝑄)))
 
Theoremxpcfucco2 49511 Value of composition in the binary product of categories of functors. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   𝑂 = (comp‘𝑇)    &   (𝜑𝐹 ∈ (𝑀(𝐵 Nat 𝐶)𝑃))    &   (𝜑𝐺 ∈ (𝑁(𝐷 Nat 𝐸)𝑄))    &   (𝜑𝐾 ∈ (𝑃(𝐵 Nat 𝐶)𝑅))    &   (𝜑𝐿 ∈ (𝑄(𝐷 Nat 𝐸)𝑆))       (𝜑 → (⟨𝐾, 𝐿⟩(⟨⟨𝑀, 𝑁⟩, ⟨𝑃, 𝑄⟩⟩𝑂𝑅, 𝑆⟩)⟨𝐹, 𝐺⟩) = ⟨(𝐾(⟨𝑀, 𝑃⟩(comp‘(𝐵 FuncCat 𝐶))𝑅)𝐹), (𝐿(⟨𝑁, 𝑄⟩(comp‘(𝐷 FuncCat 𝐸))𝑆)𝐺)⟩)
 
Theoremxpcfuccocl 49512 The composition of two natural transformations is a natural transformation. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   𝑂 = (comp‘𝑇)    &   (𝜑𝐹 ∈ (𝑀(𝐵 Nat 𝐶)𝑃))    &   (𝜑𝐺 ∈ (𝑁(𝐷 Nat 𝐸)𝑄))    &   (𝜑𝐾 ∈ (𝑃(𝐵 Nat 𝐶)𝑅))    &   (𝜑𝐿 ∈ (𝑄(𝐷 Nat 𝐸)𝑆))       (𝜑 → (⟨𝐾, 𝐿⟩(⟨⟨𝑀, 𝑁⟩, ⟨𝑃, 𝑄⟩⟩𝑂𝑅, 𝑆⟩)⟨𝐹, 𝐺⟩) ∈ ((𝑀(𝐵 Nat 𝐶)𝑅) × (𝑁(𝐷 Nat 𝐸)𝑆)))
 
Theoremxpcfucco3 49513* Value of composition in the binary product of categories of functors; expressed explicitly. (Contributed by Zhi Wang, 1-Oct-2025.)
𝑇 = ((𝐵 FuncCat 𝐶) ×c (𝐷 FuncCat 𝐸))    &   𝑂 = (comp‘𝑇)    &   (𝜑𝐹 ∈ (𝑀(𝐵 Nat 𝐶)𝑃))    &   (𝜑𝐺 ∈ (𝑁(𝐷 Nat 𝐸)𝑄))    &   (𝜑𝐾 ∈ (𝑃(𝐵 Nat 𝐶)𝑅))    &   (𝜑𝐿 ∈ (𝑄(𝐷 Nat 𝐸)𝑆))    &   𝑋 = (Base‘𝐵)    &   𝑌 = (Base‘𝐷)    &    · = (comp‘𝐶)    &    = (comp‘𝐸)       (𝜑 → (⟨𝐾, 𝐿⟩(⟨⟨𝑀, 𝑁⟩, ⟨𝑃, 𝑄⟩⟩𝑂𝑅, 𝑆⟩)⟨𝐹, 𝐺⟩) = ⟨(𝑥𝑋 ↦ ((𝐾𝑥)(⟨((1st𝑀)‘𝑥), ((1st𝑃)‘𝑥)⟩ · ((1st𝑅)‘𝑥))(𝐹𝑥))), (𝑦𝑌 ↦ ((𝐿𝑦)(⟨((1st𝑁)‘𝑦), ((1st𝑄)‘𝑦)⟩ ((1st𝑆)‘𝑦))(𝐺𝑦)))⟩)
 
21.49.15.14  Swap functors
 
Syntaxcswapf 49514 Extend class notation with the class of swap functors.
class swapF
 
Definitiondf-swapf 49515* Define the swap functor from (𝐶 ×c 𝐷) to (𝐷 ×c 𝐶) by swapping all objects (swapf1 49527) and morphisms (swapf2 49529) .

Such functor is called a "swap functor" in https://arxiv.org/pdf/2302.07810 49529 or a "twist functor" in https://arxiv.org/pdf/2508.01886 49529, the latter of which finds its counterpart as "twisting map" in https://arxiv.org/pdf/2411.04102 49529 for tensor product of algebras. The "swap functor" or "twisting map" is often denoted as a small tau 𝜏 in literature. However, the term "twist functor" is defined differently in https://arxiv.org/pdf/1208.4046 49529 and thus not adopted here.

tpos I depends on more mathbox theorems, and thus are not adopted here. See dfswapf2 49516 for an alternate definition.

(Contributed by Zhi Wang, 7-Oct-2025.)

swapF = (𝑐 ∈ V, 𝑑 ∈ V ↦ (𝑐 ×c 𝑑) / 𝑠(Base‘𝑠) / 𝑏(Hom ‘𝑠) / ⟨(𝑥𝑏 {𝑥}), (𝑢𝑏, 𝑣𝑏 ↦ (𝑓 ∈ (𝑢𝑣) ↦ {𝑓}))⟩)
 
Theoremdfswapf2 49516* Alternate definition of swapF (df-swapf 49515). (Contributed by Zhi Wang, 9-Oct-2025.)
swapF = (𝑐 ∈ V, 𝑑 ∈ V ↦ (𝑐 ×c 𝑑) / 𝑠(Base‘𝑠) / 𝑏(Hom ‘𝑠) / ⟨(tpos I ↾ 𝑏), (𝑢𝑏, 𝑣𝑏 ↦ (tpos I ↾ (𝑢𝑣)))⟩)
 
Theoremswapfval 49517* Value of the swap functor. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝐻 = (Hom ‘𝑆))       (𝜑 → (𝐶 swapF 𝐷) = ⟨(𝑥𝐵 {𝑥}), (𝑢𝐵, 𝑣𝐵 ↦ (𝑓 ∈ (𝑢𝐻𝑣) ↦ {𝑓}))⟩)
 
Theoremswapfelvv 49518 A swap functor is an ordered pair. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)       (𝜑 → (𝐶 swapF 𝐷) ∈ (V × V))
 
Theoremswapf2fvala 49519* The morphism part of the swap functor. See also swapf2fval 49520. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝐻 = (Hom ‘𝑆))       (𝜑 → (2nd ‘(𝐶 swapF 𝐷)) = (𝑢𝐵, 𝑣𝐵 ↦ (𝑓 ∈ (𝑢𝐻𝑣) ↦ {𝑓})))
 
Theoremswapf2fval 49520* The morphism part of the swap functor. See also swapf2fvala 49519. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝐻 = (Hom ‘𝑆))    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)       (𝜑𝑃 = (𝑢𝐵, 𝑣𝐵 ↦ (𝑓 ∈ (𝑢𝐻𝑣) ↦ {𝑓})))
 
Theoremswapf1vala 49521* The object part of the swap functor. See also swapf1val 49522. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)       (𝜑 → (1st ‘(𝐶 swapF 𝐷)) = (𝑥𝐵 {𝑥}))
 
Theoremswapf1val 49522* The object part of the swap functor. See also swapf1vala 49521. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)       (𝜑𝑂 = (𝑥𝐵 {𝑥}))
 
Theoremswapf2fn 49523 The morphism part of the swap functor is a function on the Cartesian square of the base set. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)       (𝜑𝑃 Fn (𝐵 × 𝐵))
 
Theoremswapf1a 49524 The object part of the swap functor swaps the objects. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)       (𝜑 → (𝑂𝑋) = ⟨(2nd𝑋), (1st𝑋)⟩)
 
Theoremswapf2vala 49525* The morphism part of the swap functor swaps the morphisms. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &   (𝜑𝑌𝐵)    &   (𝜑𝐻 = (Hom ‘𝑆))       (𝜑 → (𝑋𝑃𝑌) = (𝑓 ∈ (𝑋𝐻𝑌) ↦ {𝑓}))
 
Theoremswapf2a 49526 The morphism part of the swap functor swaps the morphisms. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &   (𝜑𝑌𝐵)    &   (𝜑𝐻 = (Hom ‘𝑆))    &   (𝜑𝐹 ∈ (𝑋𝐻𝑌))       (𝜑 → ((𝑋𝑃𝑌)‘𝐹) = ⟨(2nd𝐹), (1st𝐹)⟩)
 
Theoremswapf1 49527 The object part of the swap functor swaps the objects. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐷))       (𝜑 → (𝑋𝑂𝑌) = ⟨𝑌, 𝑋⟩)
 
Theoremswapf2val 49528* The morphism part of the swap functor swaps the morphisms. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐷))    &   (𝜑𝑍 ∈ (Base‘𝐶))    &   (𝜑𝑊 ∈ (Base‘𝐷))    &   𝑆 = (𝐶 ×c 𝐷)    &   (𝜑𝐻 = (Hom ‘𝑆))       (𝜑 → (⟨𝑋, 𝑌𝑃𝑍, 𝑊⟩) = (𝑓 ∈ (⟨𝑋, 𝑌𝐻𝑍, 𝑊⟩) ↦ {𝑓}))
 
Theoremswapf2 49529 The morphism part of the swap functor swaps the morphisms. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐷))    &   (𝜑𝑍 ∈ (Base‘𝐶))    &   (𝜑𝑊 ∈ (Base‘𝐷))    &   (𝜑𝐹 ∈ (𝑋(Hom ‘𝐶)𝑍))    &   (𝜑𝐺 ∈ (𝑌(Hom ‘𝐷)𝑊))       (𝜑 → (𝐹(⟨𝑋, 𝑌𝑃𝑍, 𝑊⟩)𝐺) = ⟨𝐺, 𝐹⟩)
 
Theoremswapf1f1o 49530 The object part of the swap functor is a bijection between base sets. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑𝐶𝑈)    &   (𝜑𝐷𝑉)    &   𝐵 = (Base‘𝑆)    &   𝐴 = (Base‘𝑇)       (𝜑𝑂:𝐵1-1-onto𝐴)
 
Theoremswapf2f1o 49531 The morphism part of the swap functor is a bijection between hom-sets. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   𝐻 = (Hom ‘𝑆)    &   𝐽 = (Hom ‘𝑇)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐷))    &   (𝜑𝑍 ∈ (Base‘𝐶))    &   (𝜑𝑊 ∈ (Base‘𝐷))       (𝜑 → (⟨𝑋, 𝑌𝑃𝑍, 𝑊⟩):(⟨𝑋, 𝑌𝐻𝑍, 𝑊⟩)–1-1-onto→(⟨𝑌, 𝑋𝐽𝑊, 𝑍⟩))
 
Theoremswapf2f1oa 49532 The morphism part of the swap functor is a bijection between hom-sets. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   𝐻 = (Hom ‘𝑆)    &   𝐽 = (Hom ‘𝑇)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &   (𝜑𝑌𝐵)       (𝜑 → (𝑋𝑃𝑌):(𝑋𝐻𝑌)–1-1-onto→((𝑂𝑋)𝐽(𝑂𝑌)))
 
Theoremswapf2f1oaALT 49533 Alternate proof of swapf2f1oa 49532. (Contributed by Zhi Wang, 8-Oct-2025.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   𝐻 = (Hom ‘𝑆)    &   𝐽 = (Hom ‘𝑇)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &   (𝜑𝑌𝐵)       (𝜑 → (𝑋𝑃𝑌):(𝑋𝐻𝑌)–1-1-onto→((𝑂𝑋)𝐽(𝑂𝑌)))
 
Theoremswapfid 49534 Each identity morphism in the source category is mapped to the corresponding identity morphism in the target category. See also swapfida 49535. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐷))    &    1 = (Id‘𝑆)    &   𝐼 = (Id‘𝑇)       (𝜑 → ((⟨𝑋, 𝑌𝑃𝑋, 𝑌⟩)‘( 1 ‘⟨𝑋, 𝑌⟩)) = (𝐼‘(𝑂‘⟨𝑋, 𝑌⟩)))
 
Theoremswapfida 49535 Each identity morphism in the source category is mapped to the corresponding identity morphism in the target category. See also swapfid 49534. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &    1 = (Id‘𝑆)    &   𝐼 = (Id‘𝑇)       (𝜑 → ((𝑋𝑃𝑋)‘( 1𝑋)) = (𝐼‘(𝑂𝑋)))
 
Theoremswapfcoa 49536 Composition in the source category is mapped to composition in the target. (𝜑𝐶 ∈ Cat) and (𝜑𝐷 ∈ Cat) can be replaced by a weaker hypothesis (𝜑𝑆 ∈ Cat). (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)    &   𝐵 = (Base‘𝑆)    &   (𝜑𝑋𝐵)    &   (𝜑𝑌𝐵)    &   (𝜑𝑍𝐵)    &   𝐻 = (Hom ‘𝑆)    &   (𝜑𝑀 ∈ (𝑋𝐻𝑌))    &   (𝜑𝑁 ∈ (𝑌𝐻𝑍))    &    · = (comp‘𝑆)    &    = (comp‘𝑇)       (𝜑 → ((𝑋𝑃𝑍)‘(𝑁(⟨𝑋, 𝑌· 𝑍)𝑀)) = (((𝑌𝑃𝑍)‘𝑁)(⟨(𝑂𝑋), (𝑂𝑌)⟩ (𝑂𝑍))((𝑋𝑃𝑌)‘𝑀)))
 
Theoremswapffunc 49537 The swap functor is a functor. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)       (𝜑𝑂(𝑆 Func 𝑇)𝑃)
 
Theoremswapfffth 49538 The swap functor is a fully faithful functor. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   (𝜑 → (𝐶 swapF 𝐷) = ⟨𝑂, 𝑃⟩)       (𝜑𝑂((𝑆 Full 𝑇) ∩ (𝑆 Faith 𝑇))𝑃)
 
Theoremswapffunca 49539 The swap functor is a functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)       (𝜑 → (𝐶 swapF 𝐷) ∈ (𝑆 Func 𝑇))
 
Theoremswapfiso 49540 The swap functor is an isomorphism between product categories. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   𝐸 = (CatCat‘𝑈)    &   (𝜑𝑈𝑉)    &   (𝜑𝑆𝑈)    &   (𝜑𝑇𝑈)    &   𝐼 = (Iso‘𝐸)       (𝜑 → (𝐶 swapF 𝐷) ∈ (𝑆𝐼𝑇))
 
Theoremswapciso 49541 The product category is categorically isomorphic to the swapped product category. (Contributed by Zhi Wang, 8-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝑆 = (𝐶 ×c 𝐷)    &   𝑇 = (𝐷 ×c 𝐶)    &   𝐸 = (CatCat‘𝑈)    &   (𝜑𝑈𝑉)    &   (𝜑𝑆𝑈)    &   (𝜑𝑇𝑈)       (𝜑𝑆( ≃𝑐𝐸)𝑇)
 
21.49.15.15  Functor evaluation
 
Theoremoppc1stflem 49542* A utility theorem for proving theorems on projection functors of opposite categories. (Contributed by Zhi Wang, 19-Nov-2025.)
𝑂 = (oppCat‘𝐶)    &   𝑃 = (oppCat‘𝐷)    &   (𝜑𝐶𝑉)    &   (𝜑𝐷𝑊)    &   ((𝜑 ∧ (𝐶 ∈ Cat ∧ 𝐷 ∈ Cat)) → ( oppFunc ‘(𝐶𝐹𝐷)) = (𝑂𝐹𝑃))    &   𝐹 = (𝑐 ∈ Cat, 𝑑 ∈ Cat ↦ 𝑌)       (𝜑 → ( oppFunc ‘(𝐶𝐹𝐷)) = (𝑂𝐹𝑃))
 
Theoremoppc1stf 49543 The opposite functor of the first projection functor is the first projection functor of opposite categories. (Contributed by Zhi Wang, 19-Nov-2025.)
𝑂 = (oppCat‘𝐶)    &   𝑃 = (oppCat‘𝐷)    &   (𝜑𝐶𝑉)    &   (𝜑𝐷𝑊)       (𝜑 → ( oppFunc ‘(𝐶 1stF 𝐷)) = (𝑂 1stF 𝑃))
 
Theoremoppc2ndf 49544 The opposite functor of the second projection functor is the second projection functor of opposite categories. (Contributed by Zhi Wang, 19-Nov-2025.)
𝑂 = (oppCat‘𝐶)    &   𝑃 = (oppCat‘𝐷)    &   (𝜑𝐶𝑉)    &   (𝜑𝐷𝑊)       (𝜑 → ( oppFunc ‘(𝐶 2ndF 𝐷)) = (𝑂 2ndF 𝑃))
 
Theorem1stfpropd 49545 If two categories have the same set of objects, morphisms, and compositions, then they have same first projection functors. (Contributed by Zhi Wang, 20-Nov-2025.)
(𝜑 → (Homf𝐴) = (Homf𝐵))    &   (𝜑 → (compf𝐴) = (compf𝐵))    &   (𝜑 → (Homf𝐶) = (Homf𝐷))    &   (𝜑 → (compf𝐶) = (compf𝐷))    &   (𝜑𝐴 ∈ Cat)    &   (𝜑𝐵 ∈ Cat)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)       (𝜑 → (𝐴 1stF 𝐶) = (𝐵 1stF 𝐷))
 
Theorem2ndfpropd 49546 If two categories have the same set of objects, morphisms, and compositions, then they have same second projection functors. (Contributed by Zhi Wang, 20-Nov-2025.)
(𝜑 → (Homf𝐴) = (Homf𝐵))    &   (𝜑 → (compf𝐴) = (compf𝐵))    &   (𝜑 → (Homf𝐶) = (Homf𝐷))    &   (𝜑 → (compf𝐶) = (compf𝐷))    &   (𝜑𝐴 ∈ Cat)    &   (𝜑𝐵 ∈ Cat)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)       (𝜑 → (𝐴 2ndF 𝐶) = (𝐵 2ndF 𝐷))
 
Theoremdiagpropd 49547 If two categories have the same set of objects, morphisms, and compositions, then they have same diagonal functors. (Contributed by Zhi Wang, 20-Nov-2025.)
(𝜑 → (Homf𝐴) = (Homf𝐵))    &   (𝜑 → (compf𝐴) = (compf𝐵))    &   (𝜑 → (Homf𝐶) = (Homf𝐷))    &   (𝜑 → (compf𝐶) = (compf𝐷))    &   (𝜑𝐴 ∈ Cat)    &   (𝜑𝐵 ∈ Cat)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)       (𝜑 → (𝐴Δfunc𝐶) = (𝐵Δfunc𝐷))
 
21.49.15.16  Transposed curry functors
 
Theoremcofuswapfcl 49548 The bifunctor pre-composed with a swap functor is a bifunctor. (Contributed by Zhi Wang, 10-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝐺 = (𝐹func (𝐶 swapF 𝐷)))       (𝜑𝐺 ∈ ((𝐶 ×c 𝐷) Func 𝐸))
 
Theoremcofuswapf1 49549 The object part of a bifunctor pre-composed with a swap functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝐺 = (𝐹func (𝐶 swapF 𝐷)))    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐵)       (𝜑 → (𝑋(1st𝐺)𝑌) = (𝑌(1st𝐹)𝑋))
 
Theoremcofuswapf2 49550 The morphism part of a bifunctor pre-composed with a swap functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝐺 = (𝐹func (𝐶 swapF 𝐷)))    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐵)    &   (𝜑𝑍𝐴)    &   (𝜑𝑊𝐵)    &   𝐻 = (Hom ‘𝐶)    &   𝐽 = (Hom ‘𝐷)    &   (𝜑𝑀 ∈ (𝑋𝐻𝑍))    &   (𝜑𝑁 ∈ (𝑌𝐽𝑊))       (𝜑 → (𝑀(⟨𝑋, 𝑌⟩(2nd𝐺)⟨𝑍, 𝑊⟩)𝑁) = (𝑁(⟨𝑌, 𝑋⟩(2nd𝐹)⟨𝑊, 𝑍⟩)𝑀))
 
Theoremtposcurf1cl 49551 The partially evaluated transposed curry functor is a functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝑋𝐴)    &   (𝜑𝐾 = ((1st𝐺)‘𝑋))       (𝜑𝐾 ∈ (𝐷 Func 𝐸))
 
Theoremtposcurf11 49552 Value of the double evaluated transposed curry functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝑋𝐴)    &   (𝜑𝐾 = ((1st𝐺)‘𝑋))    &   𝐵 = (Base‘𝐷)    &   (𝜑𝑌𝐵)       (𝜑 → ((1st𝐾)‘𝑌) = (𝑌(1st𝐹)𝑋))
 
Theoremtposcurf12 49553 The partially evaluated transposed curry functor at a morphism. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝑋𝐴)    &   (𝜑𝐾 = ((1st𝐺)‘𝑋))    &   𝐵 = (Base‘𝐷)    &   (𝜑𝑌𝐵)    &   𝐽 = (Hom ‘𝐷)    &    1 = (Id‘𝐶)    &   (𝜑𝑍𝐵)    &   (𝜑𝐻 ∈ (𝑌𝐽𝑍))       (𝜑 → ((𝑌(2nd𝐾)𝑍)‘𝐻) = (𝐻(⟨𝑌, 𝑋⟩(2nd𝐹)⟨𝑍, 𝑋⟩)( 1𝑋)))
 
Theoremtposcurf1 49554* Value of the object part of the transposed curry functor. (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   (𝜑𝑋𝐴)    &   (𝜑𝐾 = ((1st𝐺)‘𝑋))    &   𝐵 = (Base‘𝐷)    &   𝐽 = (Hom ‘𝐷)    &    1 = (Id‘𝐶)       (𝜑𝐾 = ⟨(𝑦𝐵 ↦ (𝑦(1st𝐹)𝑋)), (𝑦𝐵, 𝑧𝐵 ↦ (𝑔 ∈ (𝑦𝐽𝑧) ↦ (𝑔(⟨𝑦, 𝑋⟩(2nd𝐹)⟨𝑧, 𝑋⟩)( 1𝑋))))⟩)
 
Theoremtposcurf2 49555* Value of the transposed curry functor at a morphism. (Contributed by Zhi Wang, 10-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   𝐵 = (Base‘𝐷)    &   𝐻 = (Hom ‘𝐶)    &   𝐼 = (Id‘𝐷)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   (𝜑𝐾 ∈ (𝑋𝐻𝑌))    &   (𝜑𝐿 = ((𝑋(2nd𝐺)𝑌)‘𝐾))       (𝜑𝐿 = (𝑧𝐵 ↦ ((𝐼𝑧)(⟨𝑧, 𝑋⟩(2nd𝐹)⟨𝑧, 𝑌⟩)𝐾)))
 
Theoremtposcurf2val 49556 Value of a component of the transposed curry functor natural transformation. (Contributed by Zhi Wang, 10-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   𝐵 = (Base‘𝐷)    &   𝐻 = (Hom ‘𝐶)    &   𝐼 = (Id‘𝐷)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   (𝜑𝐾 ∈ (𝑋𝐻𝑌))    &   (𝜑𝐿 = ((𝑋(2nd𝐺)𝑌)‘𝐾))    &   (𝜑𝑍𝐵)       (𝜑 → (𝐿𝑍) = ((𝐼𝑍)(⟨𝑍, 𝑋⟩(2nd𝐹)⟨𝑍, 𝑌⟩)𝐾))
 
Theoremtposcurf2cl 49557 The transposed curry functor at a morphism is a natural transformation. (Contributed by Zhi Wang, 10-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝐴 = (Base‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))    &   𝐵 = (Base‘𝐷)    &   𝐻 = (Hom ‘𝐶)    &   𝐼 = (Id‘𝐷)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   (𝜑𝐾 ∈ (𝑋𝐻𝑌))    &   (𝜑𝐿 = ((𝑋(2nd𝐺)𝑌)‘𝐾))    &   𝑁 = (𝐷 Nat 𝐸)       (𝜑𝐿 ∈ (((1st𝐺)‘𝑋)𝑁((1st𝐺)‘𝑌)))
 
Theoremtposcurfcl 49558 The transposed curry functor of a functor 𝐹:𝐷 × 𝐶𝐸 is a functor tposcurry (𝐹):𝐶⟶(𝐷𝐸). (Contributed by Zhi Wang, 9-Oct-2025.)
(𝜑𝐺 = (⟨𝐶, 𝐷⟩ curryF (𝐹func (𝐶 swapF 𝐷))))    &   𝑄 = (𝐷 FuncCat 𝐸)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝐹 ∈ ((𝐷 ×c 𝐶) Func 𝐸))       (𝜑𝐺 ∈ (𝐶 Func 𝑄))
 
21.49.15.17  Constant functors
 
Theoremdiag1 49559* The constant functor of 𝑋. Example 3.20(2) of [Adamek] p. 30. (Contributed by Zhi Wang, 17-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝐴 = (Base‘𝐶)    &   (𝜑𝑋𝐴)    &   𝐾 = ((1st𝐿)‘𝑋)    &   𝐵 = (Base‘𝐷)    &   𝐽 = (Hom ‘𝐷)    &    1 = (Id‘𝐶)       (𝜑𝐾 = ⟨(𝑦𝐵𝑋), (𝑦𝐵, 𝑧𝐵 ↦ (𝑓 ∈ (𝑦𝐽𝑧) ↦ ( 1𝑋)))⟩)
 
Theoremdiag1a 49560* The constant functor of 𝑋. (Contributed by Zhi Wang, 19-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝐴 = (Base‘𝐶)    &   (𝜑𝑋𝐴)    &   𝐾 = ((1st𝐿)‘𝑋)    &   𝐵 = (Base‘𝐷)    &   𝐽 = (Hom ‘𝐷)    &    1 = (Id‘𝐶)       (𝜑𝐾 = ⟨(𝐵 × {𝑋}), (𝑦𝐵, 𝑧𝐵 ↦ ((𝑦𝐽𝑧) × {( 1𝑋)}))⟩)
 
Theoremdiag1f1lem 49561 The object part of the diagonal functor is 1-1 if 𝐵 is non-empty. Note that (𝜑 → (𝑀 = 𝑁𝑋 = 𝑌)) also holds because of diag1f1 49562 and f1fveq 7208. (Contributed by Zhi Wang, 19-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   (𝜑𝐵 ≠ ∅)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   𝑀 = ((1st𝐿)‘𝑋)    &   𝑁 = ((1st𝐿)‘𝑌)       (𝜑 → (𝑀 = 𝑁𝑋 = 𝑌))
 
Theoremdiag1f1 49562 The object part of the diagonal functor is 1-1 if 𝐵 is non-empty. (Contributed by Zhi Wang, 19-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   (𝜑𝐵 ≠ ∅)       (𝜑 → (1st𝐿):𝐴1-1→(𝐷 Func 𝐶))
 
Theoremdiag2f1lem 49563 Lemma for diag2f1 49564. The converse is trivial (fveq2 6834). (Contributed by Zhi Wang, 21-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   𝐻 = (Hom ‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   (𝜑𝐵 ≠ ∅)    &   (𝜑𝐹 ∈ (𝑋𝐻𝑌))    &   (𝜑𝐺 ∈ (𝑋𝐻𝑌))       (𝜑 → (((𝑋(2nd𝐿)𝑌)‘𝐹) = ((𝑋(2nd𝐿)𝑌)‘𝐺) → 𝐹 = 𝐺))
 
Theoremdiag2f1 49564 If 𝐵 is non-empty, the morphism part of a diagonal functor is injective functions from hom-sets into sets of natural transformations. (Contributed by Zhi Wang, 21-Oct-2025.)
𝐿 = (𝐶Δfunc𝐷)    &   𝐴 = (Base‘𝐶)    &   𝐵 = (Base‘𝐷)    &   𝐻 = (Hom ‘𝐶)    &   (𝜑𝐶 ∈ Cat)    &   (𝜑𝐷 ∈ Cat)    &   (𝜑𝑋𝐴)    &   (𝜑𝑌𝐴)    &   (𝜑𝐵 ≠ ∅)    &   𝑁 = (𝐷 Nat 𝐶)       (𝜑 → (𝑋(2nd𝐿)𝑌):(𝑋𝐻𝑌)–1-1→(((1st𝐿)‘𝑋)𝑁((1st𝐿)‘𝑌)))
 
21.49.15.18  Functor composition bifunctors
 
Theoremfucofulem1 49565 Lemma for proving functor theorems. (Contributed by Zhi Wang, 25-Sep-2025.)
(𝜑 → (𝜓 ↔ (𝜒𝜃𝜏)))    &   ((𝜑 ∧ (𝜃𝜏)) → 𝜂)    &   𝜒    &   ((𝜑𝜂) → 𝜃)    &   ((𝜑𝜂) → 𝜏)       (𝜑 → (𝜓𝜂))
 
Theoremfucofulem2 49566* Lemma for proving functor theorems. Maybe consider eufnfv 7175 to prove the uniqueness of a functor. (Contributed by Zhi Wang, 25-Sep-2025.)
𝐵 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷))    &   𝐻 = (Hom ‘((𝐷 FuncCat 𝐸) ×c (𝐶 FuncCat 𝐷)))       (𝐺X𝑧 ∈ (𝐵 × 𝐵)(((𝐹‘(1st𝑧))(𝐶 Nat 𝐸)(𝐹‘(2nd𝑧))) ↑m (𝐻𝑧)) ↔ (𝐺 = (𝑢𝐵, 𝑣𝐵 ↦ (𝑢𝐺𝑣)) ∧ ∀𝑚𝐵𝑛𝐵 ((𝑚𝐺𝑛) = (𝑏 ∈ ((1st𝑚)(𝐷 Nat 𝐸)(1st𝑛)), 𝑎 ∈ ((2nd𝑚)(𝐶 Nat 𝐷)(2nd𝑛)) ↦ (𝑏(𝑚𝐺𝑛)𝑎)) ∧ ∀𝑝 ∈ ((1st𝑚)(𝐷 Nat 𝐸)(1st𝑛))∀𝑞 ∈ ((2nd𝑚)(𝐶 Nat 𝐷)(2nd𝑛))(𝑝(𝑚𝐺𝑛)𝑞) ∈ ((𝐹𝑚)(𝐶 Nat 𝐸)(𝐹𝑛)))))
 
Theoremfuco2el 49567 Equivalence of product functor. (Contributed by Zhi Wang, 29-Sep-2025.)
(⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩ ∈ (𝑆 × 𝑅) ↔ (𝐾𝑆𝐿𝐹𝑅𝐺))
 
Theoremfuco2eld 49568 Equivalence of product functor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝑊 = (𝑆 × 𝑅))    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝐾𝑆𝐿)    &   (𝜑𝐹𝑅𝐺)       (𝜑𝑈𝑊)
 
Theoremfuco2eld2 49569 Equivalence of product functor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝑊 = (𝑆 × 𝑅))    &   (𝜑𝑈𝑊)    &   Rel 𝑆    &   Rel 𝑅       (𝜑𝑈 = ⟨⟨(1st ‘(1st𝑈)), (2nd ‘(1st𝑈))⟩, ⟨(1st ‘(2nd𝑈)), (2nd ‘(2nd𝑈))⟩⟩)
 
Theoremfuco2eld3 49570 Equivalence of product functor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝑊 = (𝑆 × 𝑅))    &   (𝜑𝑈𝑊)    &   Rel 𝑆    &   Rel 𝑅       (𝜑 → ((1st ‘(1st𝑈))𝑆(2nd ‘(1st𝑈)) ∧ (1st ‘(2nd𝑈))𝑅(2nd ‘(2nd𝑈))))
 
Syntaxcfuco 49571 Extend class notation with functor composition bifunctors.
class F
 
Definitiondf-fuco 49572* Definition of functor composition bifunctors. Given three categories 𝐶, 𝐷, and 𝐸, (⟨𝐶, 𝐷⟩ ∘F 𝐸) is a functor from the product category of two categories of functors to a category of functors (fucofunc 49614). The object part maps two functors to their composition (fuco11 49581 and fuco11b 49592). The morphism part defines the "composition" of two natural transformations (fuco22 49594) into another natural transformation (fuco22nat 49601) such that a "cube-like" diagram commutes. The naturality property also gives an alternate definition (fuco23a 49607). Note that such "composition" is different from fucco 17889 because they "compose" along different "axes". (Contributed by Zhi Wang, 29-Sep-2025.)
F = (𝑝 ∈ V, 𝑒 ∈ V ↦ (1st𝑝) / 𝑐(2nd𝑝) / 𝑑((𝑑 Func 𝑒) × (𝑐 Func 𝑑)) / 𝑤⟨( ∘func𝑤), (𝑢𝑤, 𝑣𝑤(1st ‘(2nd𝑢)) / 𝑓(1st ‘(1st𝑢)) / 𝑘(2nd ‘(1st𝑢)) / 𝑙(1st ‘(2nd𝑣)) / 𝑚(1st ‘(1st𝑣)) / 𝑟(𝑏 ∈ ((1st𝑢)(𝑑 Nat 𝑒)(1st𝑣)), 𝑎 ∈ ((2nd𝑢)(𝑐 Nat 𝑑)(2nd𝑣)) ↦ (𝑥 ∈ (Base‘𝑐) ↦ ((𝑏‘(𝑚𝑥))(⟨(𝑘‘(𝑓𝑥)), (𝑘‘(𝑚𝑥))⟩(comp‘𝑒)(𝑟‘(𝑚𝑥)))(((𝑓𝑥)𝑙(𝑚𝑥))‘(𝑎𝑥))))))⟩)
 
Theoremfucofvalg 49573* Value of the function giving the functor composition bifunctor. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑𝑃𝑈)    &   (𝜑 → (1st𝑃) = 𝐶)    &   (𝜑 → (2nd𝑃) = 𝐷)    &   (𝜑𝐸𝑉)    &   (𝜑 → (𝑃F 𝐸) = )    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑 = ⟨( ∘func𝑊), (𝑢𝑊, 𝑣𝑊(1st ‘(2nd𝑢)) / 𝑓(1st ‘(1st𝑢)) / 𝑘(2nd ‘(1st𝑢)) / 𝑙(1st ‘(2nd𝑣)) / 𝑚(1st ‘(1st𝑣)) / 𝑟(𝑏 ∈ ((1st𝑢)(𝐷 Nat 𝐸)(1st𝑣)), 𝑎 ∈ ((2nd𝑢)(𝐶 Nat 𝐷)(2nd𝑣)) ↦ (𝑥 ∈ (Base‘𝐶) ↦ ((𝑏‘(𝑚𝑥))(⟨(𝑘‘(𝑓𝑥)), (𝑘‘(𝑚𝑥))⟩(comp‘𝐸)(𝑟‘(𝑚𝑥)))(((𝑓𝑥)𝑙(𝑚𝑥))‘(𝑎𝑥))))))⟩)
 
Theoremfucofval 49574* Value of the function giving the functor composition bifunctor. Hypotheses fucofval.c and fucofval.d are not redundant (fucofvalne 49580). (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = )    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑 = ⟨( ∘func𝑊), (𝑢𝑊, 𝑣𝑊(1st ‘(2nd𝑢)) / 𝑓(1st ‘(1st𝑢)) / 𝑘(2nd ‘(1st𝑢)) / 𝑙(1st ‘(2nd𝑣)) / 𝑚(1st ‘(1st𝑣)) / 𝑟(𝑏 ∈ ((1st𝑢)(𝐷 Nat 𝐸)(1st𝑣)), 𝑎 ∈ ((2nd𝑢)(𝐶 Nat 𝐷)(2nd𝑣)) ↦ (𝑥 ∈ (Base‘𝐶) ↦ ((𝑏‘(𝑚𝑥))(⟨(𝑘‘(𝑓𝑥)), (𝑘‘(𝑚𝑥))⟩(comp‘𝐸)(𝑟‘(𝑚𝑥)))(((𝑓𝑥)𝑙(𝑚𝑥))‘(𝑎𝑥))))))⟩)
 
Theoremfucoelvv 49575 A functor composition bifunctor is an ordered pair. Enables 1st2ndb 7973. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = )       (𝜑 ∈ (V × V))
 
Theoremfuco1 49576 The object part of the functor composition bifunctor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑𝑂 = ( ∘func𝑊))
 
Theoremfucof1 49577 The object part of the functor composition bifunctor maps ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)) into (𝐶 Func 𝐸). (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑𝑂:𝑊⟶(𝐶 Func 𝐸))
 
Theoremfuco2 49578* The morphism part of the functor composition bifunctor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑𝑃 = (𝑢𝑊, 𝑣𝑊(1st ‘(2nd𝑢)) / 𝑓(1st ‘(1st𝑢)) / 𝑘(2nd ‘(1st𝑢)) / 𝑙(1st ‘(2nd𝑣)) / 𝑚(1st ‘(1st𝑣)) / 𝑟(𝑏 ∈ ((1st𝑢)(𝐷 Nat 𝐸)(1st𝑣)), 𝑎 ∈ ((2nd𝑢)(𝐶 Nat 𝐷)(2nd𝑣)) ↦ (𝑥 ∈ (Base‘𝐶) ↦ ((𝑏‘(𝑚𝑥))(⟨(𝑘‘(𝑓𝑥)), (𝑘‘(𝑚𝑥))⟩(comp‘𝐸)(𝑟‘(𝑚𝑥)))(((𝑓𝑥)𝑙(𝑚𝑥))‘(𝑎𝑥)))))))
 
Theoremfucofn2 49579 The morphism part of the functor composition bifunctor is a function on the Cartesian square of the base set. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑𝐶𝑇)    &   (𝜑𝐷𝑈)    &   (𝜑𝐸𝑉)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑𝑃 Fn (𝑊 × 𝑊))
 
Theoremfucofvalne 49580* Value of the function giving the functor composition bifunctor, if 𝐶 or 𝐷 are not sets. (Contributed by Zhi Wang, 7-Oct-2025.)
(𝜑 → ¬ (𝐶 ∈ V ∧ 𝐷 ∈ V))    &   (𝜑𝐸 ∈ Cat)    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = )    &   (𝜑𝑊 = ((𝐷 Func 𝐸) × (𝐶 Func 𝐷)))       (𝜑 ≠ ⟨( ∘func𝑊), (𝑢𝑊, 𝑣𝑊(1st ‘(2nd𝑢)) / 𝑓(1st ‘(1st𝑢)) / 𝑘(2nd ‘(1st𝑢)) / 𝑙(1st ‘(2nd𝑣)) / 𝑚(1st ‘(1st𝑣)) / 𝑟(𝑏 ∈ ((1st𝑢)(𝐷 Nat 𝐸)(1st𝑣)), 𝑎 ∈ ((2nd𝑢)(𝐶 Nat 𝐷)(2nd𝑣)) ↦ (𝑥 ∈ (Base‘𝐶) ↦ ((𝑏‘(𝑚𝑥))(⟨(𝑘‘(𝑓𝑥)), (𝑘‘(𝑚𝑥))⟩(comp‘𝐸)(𝑟‘(𝑚𝑥)))(((𝑓𝑥)𝑙(𝑚𝑥))‘(𝑎𝑥))))))⟩)
 
Theoremfuco11 49581 The object part of the functor composition bifunctor maps two functors to their composition. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)       (𝜑 → (𝑂𝑈) = (⟨𝐾, 𝐿⟩ ∘func𝐹, 𝐺⟩))
 
Theoremfuco11cl 49582 The object part of the functor composition bifunctor maps into (𝐶 Func 𝐸). (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)       (𝜑 → (𝑂𝑈) ∈ (𝐶 Func 𝐸))
 
Theoremfuco11a 49583* The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   𝐵 = (Base‘𝐶)       (𝜑 → (𝑂𝑈) = ⟨(𝐾𝐹), (𝑥𝐵, 𝑦𝐵 ↦ (((𝐹𝑥)𝐿(𝐹𝑦)) ∘ (𝑥𝐺𝑦)))⟩)
 
Theoremfuco112 49584* The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly for the morphism part of the composed functor. (Contributed by Zhi Wang, 3-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   𝐵 = (Base‘𝐶)       (𝜑 → (2nd ‘(𝑂𝑈)) = (𝑥𝐵, 𝑦𝐵 ↦ (((𝐹𝑥)𝐿(𝐹𝑦)) ∘ (𝑥𝐺𝑦))))
 
Theoremfuco111 49585 The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly for the object part of the composed functor. (Contributed by Zhi Wang, 2-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)       (𝜑 → (1st ‘(𝑂𝑈)) = (𝐾𝐹))
 
Theoremfuco111x 49586 The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly for the object part of the composed functor. An object is mapped by two functors in succession. (Contributed by Zhi Wang, 3-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))       (𝜑 → ((1st ‘(𝑂𝑈))‘𝑋) = (𝐾‘(𝐹𝑋)))
 
Theoremfuco112x 49587 The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly for the morphism part of the composed functor. (Contributed by Zhi Wang, 3-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐶))       (𝜑 → (𝑋(2nd ‘(𝑂𝑈))𝑌) = (((𝐹𝑋)𝐿(𝐹𝑌)) ∘ (𝑋𝐺𝑌)))
 
Theoremfuco112xa 49588 The object part of the functor composition bifunctor maps two functors to their composition, expressed explicitly for the morphism part of the composed functor. A morphism is mapped by two functors in succession. (Contributed by Zhi Wang, 3-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐶))    &   (𝜑𝐴 ∈ (𝑋(Hom ‘𝐶)𝑌))       (𝜑 → ((𝑋(2nd ‘(𝑂𝑈))𝑌)‘𝐴) = (((𝐹𝑋)𝐿(𝐹𝑌))‘((𝑋𝐺𝑌)‘𝐴)))
 
Theoremfuco11id 49589 The identity morphism of the mapped object. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   𝑄 = (𝐶 FuncCat 𝐸)    &   𝐼 = (Id‘𝑄)    &    1 = (Id‘𝐸)       (𝜑 → (𝐼‘(𝑂𝑈)) = ( 1 ∘ (𝐾𝐹)))
 
Theoremfuco11idx 49590 The identity morphism of the mapped object. (Contributed by Zhi Wang, 3-Oct-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   𝑄 = (𝐶 FuncCat 𝐸)    &   𝐼 = (Id‘𝑄)    &    1 = (Id‘𝐸)    &   (𝜑𝑋 ∈ (Base‘𝐶))       (𝜑 → ((𝐼‘(𝑂𝑈))‘𝑋) = ( 1 ‘(𝐾‘(𝐹𝑋))))
 
Theoremfuco21 49591* The morphism part of the functor composition bifunctor. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐹(𝐶 Func 𝐷)𝐺)    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑀(𝐶 Func 𝐷)𝑁)    &   (𝜑𝑅(𝐷 Func 𝐸)𝑆)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)       (𝜑 → (𝑈𝑃𝑉) = (𝑏 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩), 𝑎 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩) ↦ (𝑥 ∈ (Base‘𝐶) ↦ ((𝑏‘(𝑀𝑥))(⟨(𝐾‘(𝐹𝑥)), (𝐾‘(𝑀𝑥))⟩(comp‘𝐸)(𝑅‘(𝑀𝑥)))(((𝐹𝑥)𝐿(𝑀𝑥))‘(𝑎𝑥))))))
 
Theoremfuco11b 49592 The object part of the functor composition bifunctor maps two functors to their composition. (Contributed by Zhi Wang, 11-Oct-2025.)
(𝜑 → (1st ‘(⟨𝐶, 𝐷⟩ ∘F 𝐸)) = 𝑂)    &   (𝜑𝐹 ∈ (𝐶 Func 𝐷))    &   (𝜑𝐺 ∈ (𝐷 Func 𝐸))       (𝜑 → (𝐺𝑂𝐹) = (𝐺func 𝐹))
 
Theoremfuco11bALT 49593 Alternate proof of fuco11b 49592. (Contributed by Zhi Wang, 11-Oct-2025.) (Proof modification is discouraged.) (New usage is discouraged.)
(𝜑 → (1st ‘(⟨𝐶, 𝐷⟩ ∘F 𝐸)) = 𝑂)    &   (𝜑𝐹 ∈ (𝐶 Func 𝐷))    &   (𝜑𝐺 ∈ (𝐷 Func 𝐸))       (𝜑 → (𝐺𝑂𝐹) = (𝐺func 𝐹))
 
Theoremfuco22 49594* The morphism part of the functor composition bifunctor. See also fuco22a 49605. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))       (𝜑 → (𝐵(𝑈𝑃𝑉)𝐴) = (𝑥 ∈ (Base‘𝐶) ↦ ((𝐵‘(𝑀𝑥))(⟨(𝐾‘(𝐹𝑥)), (𝐾‘(𝑀𝑥))⟩(comp‘𝐸)(𝑅‘(𝑀𝑥)))(((𝐹𝑥)𝐿(𝑀𝑥))‘(𝐴𝑥)))))
 
Theoremfucofn22 49595 The morphism part of the functor composition bifunctor maps two natural transformations to a function on a base set. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))       (𝜑 → (𝐵(𝑈𝑃𝑉)𝐴) Fn (Base‘𝐶))
 
Theoremfuco23 49596 The morphism part of the functor composition bifunctor. See also fuco23a 49607. (Contributed by Zhi Wang, 29-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))    &   (𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑 = (⟨(𝐾‘(𝐹𝑋)), (𝐾‘(𝑀𝑋))⟩(comp‘𝐸)(𝑅‘(𝑀𝑋))))       (𝜑 → ((𝐵(𝑈𝑃𝑉)𝐴)‘𝑋) = ((𝐵‘(𝑀𝑋)) (((𝐹𝑋)𝐿(𝑀𝑋))‘(𝐴𝑋))))
 
Theoremfuco22natlem1 49597 Lemma for fuco22nat 49601. The commutative square of natural transformation 𝐴 in category 𝐷, mapped to category 𝐸 by the morphism part 𝐿 of the functor. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐶))    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐻 ∈ (𝑋(Hom ‘𝐶)𝑌))    &   (𝜑𝐾(𝐷 Func 𝐸)𝐿)       (𝜑 → ((((𝐹𝑌)𝐿(𝑀𝑌))‘(𝐴𝑌))(⟨(𝐾‘(𝐹𝑋)), (𝐾‘(𝐹𝑌))⟩(comp‘𝐸)(𝐾‘(𝑀𝑌)))(((𝐹𝑋)𝐿(𝐹𝑌))‘((𝑋𝐺𝑌)‘𝐻))) = ((((𝑀𝑋)𝐿(𝑀𝑌))‘((𝑋𝑁𝑌)‘𝐻))(⟨(𝐾‘(𝐹𝑋)), (𝐾‘(𝑀𝑋))⟩(comp‘𝐸)(𝐾‘(𝑀𝑌)))(((𝐹𝑋)𝐿(𝑀𝑋))‘(𝐴𝑋))))
 
Theoremfuco22natlem2 49598 Lemma for fuco22nat 49601. The commutative square of natural transformation 𝐵 in category 𝐸, combined with the commutative square of fuco22natlem1 49597. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐶))    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐻 ∈ (𝑋(Hom ‘𝐶)𝑌))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))       (𝜑 → (((𝐵‘(𝑀𝑌))(⟨(𝐾‘(𝐹𝑌)), (𝐾‘(𝑀𝑌))⟩(comp‘𝐸)(𝑅‘(𝑀𝑌)))(((𝐹𝑌)𝐿(𝑀𝑌))‘(𝐴𝑌)))(⟨(𝐾‘(𝐹𝑋)), (𝐾‘(𝐹𝑌))⟩(comp‘𝐸)(𝑅‘(𝑀𝑌)))(((𝐹𝑋)𝐿(𝐹𝑌))‘((𝑋𝐺𝑌)‘𝐻))) = ((((𝑀𝑋)𝑆(𝑀𝑌))‘((𝑋𝑁𝑌)‘𝐻))(⟨(𝐾‘(𝐹𝑋)), (𝑅‘(𝑀𝑋))⟩(comp‘𝐸)(𝑅‘(𝑀𝑌)))((𝐵‘(𝑀𝑋))(⟨(𝐾‘(𝐹𝑋)), (𝐾‘(𝑀𝑋))⟩(comp‘𝐸)(𝑅‘(𝑀𝑋)))(((𝐹𝑋)𝐿(𝑀𝑋))‘(𝐴𝑋)))))
 
Theoremfuco22natlem3 49599 Combine fuco22natlem2 49598 with fuco23 49596. (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑𝑋 ∈ (Base‘𝐶))    &   (𝜑𝑌 ∈ (Base‘𝐶))    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐻 ∈ (𝑋(Hom ‘𝐶)𝑌))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))    &   (𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)       (𝜑 → (((𝐵(𝑈𝑃𝑉)𝐴)‘𝑌)(⟨((𝐾𝐹)‘𝑋), ((𝐾𝐹)‘𝑌)⟩(comp‘𝐸)((𝑅𝑀)‘𝑌))((((𝐹𝑋)𝐿(𝐹𝑌)) ∘ (𝑋𝐺𝑌))‘𝐻)) = (((((𝑀𝑋)𝑆(𝑀𝑌)) ∘ (𝑋𝑁𝑌))‘𝐻)(⟨((𝐾𝐹)‘𝑋), ((𝑅𝑀)‘𝑋)⟩(comp‘𝐸)((𝑅𝑀)‘𝑌))((𝐵(𝑈𝑃𝑉)𝐴)‘𝑋)))
 
Theoremfuco22natlem 49600 The composed natural transformation is a natural transformation. Use fuco22nat 49601 instead. (New usage is discouraged.) (Contributed by Zhi Wang, 30-Sep-2025.)
(𝜑 → (⟨𝐶, 𝐷⟩ ∘F 𝐸) = ⟨𝑂, 𝑃⟩)    &   (𝜑𝐴 ∈ (⟨𝐹, 𝐺⟩(𝐶 Nat 𝐷)⟨𝑀, 𝑁⟩))    &   (𝜑𝐵 ∈ (⟨𝐾, 𝐿⟩(𝐷 Nat 𝐸)⟨𝑅, 𝑆⟩))    &   (𝜑𝑈 = ⟨⟨𝐾, 𝐿⟩, ⟨𝐹, 𝐺⟩⟩)    &   (𝜑𝑉 = ⟨⟨𝑅, 𝑆⟩, ⟨𝑀, 𝑁⟩⟩)       (𝜑 → (𝐵(𝑈𝑃𝑉)𝐴) ∈ ((𝑂𝑈)(𝐶 Nat 𝐸)(𝑂𝑉)))
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144 14301-14400 145 14401-14500 146 14501-14600 147 14601-14700 148 14701-14800 149 14801-14900 150 14901-15000 151 15001-15100 152 15101-15200 153 15201-15300 154 15301-15400 155 15401-15500 156 15501-15600 157 15601-15700 158 15701-15800 159 15801-15900 160 15901-16000 161 16001-16100 162 16101-16200 163 16201-16300 164 16301-16400 165 16401-16500 166 16501-16600 167 16601-16700 168 16701-16800 169 16801-16900 170 16901-17000 171 17001-17100 172 17101-17200 173 17201-17300 174 17301-17400 175 17401-17500 176 17501-17600 177 17601-17700 178 17701-17800 179 17801-17900 180 17901-18000 181 18001-18100 182 18101-18200 183 18201-18300 184 18301-18400 185 18401-18500 186 18501-18600 187 18601-18700 188 18701-18800 189 18801-18900 190 18901-19000 191 19001-19100 192 19101-19200 193 19201-19300 194 19301-19400 195 19401-19500 196 19501-19600 197 19601-19700 198 19701-19800 199 19801-19900 200 19901-20000 201 20001-20100 202 20101-20200 203 20201-20300 204 20301-20400 205 20401-20500 206 20501-20600 207 20601-20700 208 20701-20800 209 20801-20900 210 20901-21000 211 21001-21100 212 21101-21200 213 21201-21300 214 21301-21400 215 21401-21500 216 21501-21600 217 21601-21700 218 21701-21800 219 21801-21900 220 21901-22000 221 22001-22100 222 22101-22200 223 22201-22300 224 22301-22400 225 22401-22500 226 22501-22600 227 22601-22700 228 22701-22800 229 22801-22900 230 22901-23000 231 23001-23100 232 23101-23200 233 23201-23300 234 23301-23400 235 23401-23500 236 23501-23600 237 23601-23700 238 23701-23800 239 23801-23900 240 23901-24000 241 24001-24100 242 24101-24200 243 24201-24300 244 24301-24400 245 24401-24500 246 24501-24600 247 24601-24700 248 24701-24800 249 24801-24900 250 24901-25000 251 25001-25100 252 25101-25200 253 25201-25300 254 25301-25400 255 25401-25500 256 25501-25600 257 25601-25700 258 25701-25800 259 25801-25900 260 25901-26000 261 26001-26100 262 26101-26200 263 26201-26300 264 26301-26400 265 26401-26500 266 26501-26600 267 26601-26700 268 26701-26800 269 26801-26900 270 26901-27000 271 27001-27100 272 27101-27200 273 27201-27300 274 27301-27400 275 27401-27500 276 27501-27600 277 27601-27700 278 27701-27800 279 27801-27900 280 27901-28000 281 28001-28100 282 28101-28200 283 28201-28300 284 28301-28400 285 28401-28500 286 28501-28600 287 28601-28700 288 28701-28800 289 28801-28900 290 28901-29000 291 29001-29100 292 29101-29200 293 29201-29300 294 29301-29400 295 29401-29500 296 29501-29600 297 29601-29700 298 29701-29800 299 29801-29900 300 29901-30000 301 30001-30100 302 30101-30200 303 30201-30300 304 30301-30400 305 30401-30500 306 30501-30600 307 30601-30700 308 30701-30800 309 30801-30900 310 30901-31000 311 31001-31100 312 31101-31200 313 31201-31300 314 31301-31400 315 31401-31500 316 31501-31600 317 31601-31700 318 31701-31800 319 31801-31900 320 31901-32000 321 32001-32100 322 32101-32200 323 32201-32300 324 32301-32400 325 32401-32500 326 32501-32600 327 32601-32700 328 32701-32800 329 32801-32900 330 32901-33000 331 33001-33100 332 33101-33200 333 33201-33300 334 33301-33400 335 33401-33500 336 33501-33600 337 33601-33700 338 33701-33800 339 33801-33900 340 33901-34000 341 34001-34100 342 34101-34200 343 34201-34300 344 34301-34400 345 34401-34500 346 34501-34600 347 34601-34700 348 34701-34800 349 34801-34900 350 34901-35000 351 35001-35100 352 35101-35200 353 35201-35300 354 35301-35400 355 35401-35500 356 35501-35600 357 35601-35700 358 35701-35800 359 35801-35900 360 35901-36000 361 36001-36100 362 36101-36200 363 36201-36300 364 36301-36400 365 36401-36500 366 36501-36600 367 36601-36700 368 36701-36800 369 36801-36900 370 36901-37000 371 37001-37100 372 37101-37200 373 37201-37300 374 37301-37400 375 37401-37500 376 37501-37600 377 37601-37700 378 37701-37800 379 37801-37900 380 37901-38000 381 38001-38100 382 38101-38200 383 38201-38300 384 38301-38400 385 38401-38500 386 38501-38600 387 38601-38700 388 38701-38800 389 38801-38900 390 38901-39000 391 39001-39100 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