nLab enriched functor category

Idea

In the context of $V$-enriched category theory (with $V$ any suitable cosmos for enrichment) for $\mathbf{C}$, $\mathbf{D}$ a pair of $V$-enriched categories, there is, fist of all, an ordinary category whose

• objects are the enriched functors $F \colon \mathbf{C} \longrightarrow \mathbf{D}$,

• morphisms$\eta \colon F \Rightarrow F'$ are the enriched natural transformations.

This notion is a generalization of the plain notion of the functor category between locally small categories, to which it reduces in the case that $V \equiv$ Set equipped with its cartesian monoidal-structure.

As such one may and does call this ordinary category the “enriched functor category” between $\mathbf{C}$ and $\mathbf{D}$, in the sense of the “category of enriched functors”.

However, this category of enriched functors canonically enhances further to a $V$-enriched category itself, hence to an “enriched-functor enriched-category”, then traditionally often denoted $[\mathbf{C}, \mathbf{D}]$ or similar.

Namely, for $F, G \,\colon\, \mathbf{C} \longrightarrow \mathbf{D}$ a pair of $V$-enriched functors between $V$-enriched categories, the collection of enriched natural transformations from $F$ to $G$ can also be given the structure of an object in $V$, in a compatible way:

Definition

For $\mathbf{C}$ and $\mathbf{D}$ $V$-enriched categories, there is a $V$-enriched category, denoted $[\mathbf{C},\,\mathbf{D}]$, whose

• objects are the $V$-enriched functors $F \colon \mathbf{C} \longrightarrow \mathbf{D}$

• hom-objects$\;[C,D](F,G)$ between $V$-functors $F, G$ are given by the $V$-enriched end

  $$[\mathbf{C},\mathbf{D}](F,G) \;\coloneqq\; \int_{c \in \mathbf{C}} \mathbf{D}\big(F(c),\, G(c)\big)$$

  over the enriched hom-functor

  $$\mathbf{D}\big( F(-) ,\, G(-) \big) \;\colon\; \mathbf{C}^{op} \otimes \mathbf{C} \longrightarrow V \,,$$

• the composition operation

$$\circ_{K,F,G} \,\colon\, [\mathbf{C},\mathbf{D}](F,G) \otimes [\mathbf{C},\mathbf{D}](K,F) \longrightarrow [\mathbf{C},\mathbf{D}](K,G)$$

is the universal morphism into the end $[\mathbf{C},\mathbf{D}](K,F)$ obtained from observing that the composites

$$[\mathbf{C},\mathbf{D}](F,G) \otimes [\mathbf{C},\mathbf{D}](K,F) \stackrel{E_c\otimes E_d}{\longrightarrow} \mathbf{D}\big(F(c),G(c)\big) \otimes \mathbf{D}\big(K(c),F(c)\big) \stackrel{\circ_{K(c), F(c), G(c)}}{\longrightarrow} \mathbf{D}\big(K(c), F(c)\big)$$

(where $E_c \colon [\mathbf{C},\mathbf{D}](F,G) \to \mathbf{D}\big(F(c),G(c)\big)$ denotes the canonical morphism out of the end, i.e. the counit)

form an extra $V$-natural family, equivalently that

$$[\mathbf{C},\mathbf{D}](F,G) \otimes [\mathbf{C},\mathbf{D}](K,F) \stackrel {\prod_{c \in Obj(c)}E_c\otimes E_c} {\longrightarrow} \prod_{c \in Obj(c)} \mathbf{D}\big(F(c),G(c)\big) \otimes \mathbf{D}\big(K(c),\,F(c)\big) \stackrel{\prod_{c \in Obj(c)} \circ_{K(c), F(c), G(c)}}{\longrightarrow} \prod_{c \in Obj(c)} \mathbf{D}\big(K(c),\,G(c)\big)$$

equalizes the two maps appearing in the equalizer-definition of the end.

Proposition

For $V =$Set, so that $V$-enriched categories are just ordinary locally small categories, the $V$-enriched functor category coincides with the ordinary functor category. (See the examples below.)

Examples

Ordinary functor categories

To understand the role of the end here, it is useful to spell this out for the case where $V =$ Set, where we are dealing with ordinary locally small categories.

So let $V = Set$ where set is equipped with its cartesian monoidal structure.

Recall the definition of the end over

$$\mathbf{D}\big( F(-),G(-) \big) \,\colon\, \mathbf{C}^{op} \otimes \mathbf{C} \longrightarrow Set$$

as an equalizer: it is the universal subobject

$$\int_{c \in C} \mathbf{D}\big(F(c),\, G(c)\big) \hookrightarrow \prod_{c \in Obj(C)} \mathbf{D}\big(F(c),\, G(c)\big)$$

of the product of all hom-sets in $D$ between the images of objects in $C$ under the functors $F$ and $G$. So one element $\eta \in \int_{c \in \mathbf{C}} \mathbf{D}\big(F(c), G(c)\big)$ is a collection of morphisms

$$\big( F(c) \stackrel{\eta_c}{\longrightarrow} G(c) \big)_{c \in Obj(c)}$$

such that the “left and right action” (in the sense of distributors) of $\mathbf{D}\big(F(-),G(-)\big)$ on these elements coincides. Unwrapping what this action is (see the details at end) one find that

• the “right action” by a morphism $c \stackrel{f}{\to} d$ is the postcomposition $(F(c) \stackrel{\eta_c}{\to} G(c)) \mapsto (F(c) \stackrel{\eta_c}{\to} G(c) \stackrel{G(f)}{\to} G(d))$

• the “left action” by a morphism $c \stackrel{f}{\to} d$ is the precomposition $(F(d) \stackrel{\eta_d}{\to} G(d)) \mapsto (F(c) \stackrel{F(f)}{\to} F(d) \stackrel{\eta_d}{\to} G(d) )$.

So the invariants under the combined action are those $\eta$ for which for all $f \colon c \to d$ in $C$ the diagram

$$\array{ F(c) &\stackrel{\eta_c}{\longrightarrow} & G(c) \\ \Big\downarrow\mathrlap{{}^{F(f)}} && \Big\downarrow\mathrlap{{}^{G(f)}} \\ F(d) & \stackrel{\eta_d}{\longrightarrow} & G(d) }$$

commutes. Evidently, this means that the elements $\eta$ of the end $\int_{c \in \mathbf{C}} \mathbf{D}\big(F(c), G(c)\big)$ are precisely the natural transformations between $F$ and $G$.

Pointwise order

For categories enriched in truth values, the enriched functor category is given by the pointwise order.

Properties

Enhanced enrichment

It happens that a $V$-enriched functor category $Func(\mathbf{X},\mathbf{C})$ — which by the above discussion is a priori a $\mathbf{V}$-enriched category — carries an enhanced enrichment over the functor category $Func(\mathbf{X},\mathbf{V})$.

A common kind of example are categories of simplicial objects in an ordinary $Set$-enriched category – hence functor categories $Func(\Delta^{op}, C)$ on the opposite simplex category – which one wants to regard not just enriched in $Set$, but as enriched in $Func(\Delta^{op}, Set) \,\equiv\,$ sSet, namely in simplicial sets.

We may bootstrap the discussion of this situation by first considering the case where $\mathbf{C} = \mathbf{V}$ itself, where it means that $Func(\mathbf{X},\mathbf{V})$ is closed monoidal under the $\mathbf{X}$-objectwise tensor product taken in $\mathbf{V}$. In the base case where $\mathbf{V} =$ Set this reduces to the statement of the closed monoidal structure on presheaves.

Proposition

Let

• $(V, \otimes)$ be a bicomplete closed monoidal category, canonically regarded as a $V$-enriched $\mathbf{V}$

  via its internal hom $[-,-]$;

• $\mathbf{C}$ a bicomplete $V$-enriched category which is

  also $V$-tensored, via $\mathbf{V} \times \mathbf{C} \overset{(\text{-})\cdot(\text{-})}{\longrightarrow} \mathbf{C}$,

  and $V$-cotensored via $\mathbf{V}^{op} \times \mathbf{C} \overset{(\text{-})^{(\text{-})}}{\longrightarrow} \mathbf{C}$;

• $\mathbf{X}$ a small $V$-enriched category.

Then the enriched functor category…

1. …$\mathbf{V}^{\mathbf{X}} \,\coloneqq\, Func(\mathbf{X},\,\mathbf{V})$ carries closed monoidal category structure

   given by the $\mathbf{X}$-objectwise tensor product

   $$\mathcal{S}_{\mathbf{X}} ,\, \mathcal{T}_{\mathbf{X}} \,\in\, \mathbf{V}^{\mathbf{X}} \;\;\;\;\;\;\;\;\;\; \vdash \;\;\;\;\;\;\;\;\;\; \mathcal{S}_{\mathbf{X}} \otimes \mathcal{T}_{\mathbf{X}} \;\colon\; x \;\mapsto\; (\mathcal{S}_{\mathbf{X}} \otimes \mathcal{T}_{\mathbf{X}})_x \;\; \coloneqq \;\; \mathcal{S}_x \otimes \mathcal{T}_x$$

   and with corresponding internal hom given by:

   $$\mathcal{S}_{\mathbf{X}} ,\, \mathcal{T}_{\mathbf{X}} \,\in\, \mathbf{V}^{\mathbf{X}} \;\;\;\;\;\;\;\;\;\; \vdash \;\;\;\;\;\;\;\;\;\; \big[ \mathcal{S}_{\mathbf{X}} ,\, \mathcal{T}_{\mathbf{X}} \big] \;\colon\; x \;\mapsto\; \big[ \mathcal{S}_{\mathbf{X}} ,\, \mathcal{T}_{\mathbf{X}} \big]_x \;\; \coloneqq \;\; \int_{x' \in \mathbf{X}} \mathbf{V}\big( \mathbf{X}(x,x') \otimes \mathcal{S}_{x'} ,\, \mathcal{T}_{x'} \big) \,.$$

2. … $\mathbf{C}^{\mathbf{X}}$ becomes enriched, tensored and cotensored over $\mathbf{V}^{\mathbf{X}}$, via the following end-formulas, respectively:

   $$\begin{array}{rccl} \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \;\in\; \mathbf{C}^{\mathbf{X}} &\;\;\;\vdash\;\;\;& \mathbf{C}^{\mathbf{X}} \big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big) & \coloneqq\; \Big( x \,\mapsto\, \int_{x' \in \mathbf{X}} \mathbf{C}\big( \mathbf{X}(x,x') \cdot \mathscr{V}_{x'} ,\, \mathscr{W}_{x'} \big) \Big) \;\;\; \in \; \mathbf{V}^{\mathbf{X}} \\ \mathcal{S}_{\mathbf{X}} \,\in\, \mathbf{V}^{\mathbf{X}} ;\; \mathscr{V}_{\mathbf{X}} \in\, \mathbf{C}^{\mathbf{X}} &\vdash& \mathcal{S}_{\mathbf{X}} \cdot \mathscr{V}_{\mathbf{X}} & \coloneqq\; \big( x \,\mapsto\, \mathcal{S}_{x'} \cdot \mathscr{V}_{x'} \big) \;\;\; \in \; \mathbf{C}^{\mathbf{X}} \\ \mathcal{S}_{\mathbf{X}} \,\in\, \mathbf{V}^{\mathbf{X}} ;\; \mathscr{V}_{\mathbf{X}} \in\, \mathbf{C}^{\mathbf{X}} &\vdash& \big(\mathscr{V}_{\mathbf{X}}\big)^{ \mathcal{S}_{\mathbf{X}} } & \coloneqq\; \Big( x \,\mapsto\, \int_{x' \in \mathbf{X}} \big(\mathscr{W}_{x'}\big)^{ \mathbf{X}(x,x') \otimes \mathcal{S}_{x'} } \Big) \;\;\; \in \; \mathbf{C}^{\mathbf{X}} \mathrlap{\,.} \end{array}$$

Proof

Observe the following sequence of natural isomorphisms:

$$\begin{array}{ll} Func(\mathbf{X},\,\mathbf{V}) \big( \mathcal{R}_{\mathbf{X}} \;,\; [\mathcal{S}_{\mathbf{X}},\, \mathcal{T}_{\mathbf{X}}] \big) \\ \;\simeq\; \int_{x \in \mathbf{X}} \mathbf{V} \Big( \mathcal{R}_{x} \;,\; \int_{y \in \mathbf{X}} \mathbf{V} \big( \mathbf{X}(x,y) \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \big) \Big) & \text{by the definitions} \\ \;\simeq\; \int_{x \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{V} \Big( \mathcal{R}_{x} \;,\; \mathbf{V} \big( \mathbf{X}(x,y) \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \big) \Big) & \text{ since internal homs preserve limits } \\ \;\simeq\; \int_{x \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{V} \Big( \mathbf{X}(x,y) \otimes \mathcal{R}_{x} \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \Big) & \text{by closed monoidal structure of}\;\mathbf{V} \\ \;\simeq\; \int_{y \in \mathbf{X}} \int_{x \in \mathbf{X}} \mathbf{V} \Big( \mathbf{X}(x,y) \otimes \mathcal{R}_{x} \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \Big) & \text{ by Fubini theorem for ends } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{V} \Big( \big( \int^{x \in \mathbf{X}} \mathbf{X}(x,y) \otimes \mathcal{R}_{x} \big) \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \Big) & \text{ since internal homs preserve limits } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{V} \Big( \mathcal{R}_{y} \otimes \mathcal{S}_{y} \;,\; \mathcal{T}_{y} \Big) & \text{ by co-Yoneda lemma } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{V} \Big( \big( \mathcal{R}_{\mathbf{X}} \otimes \mathcal{S}_{\mathbf{X}} \big)_{y} \;,\; \mathcal{T}_{y} \Big) & \text{ by definition } \\ \;\simeq\; Func(\mathbf{X},\mathbf{V}) \big( \mathcal{R}_{\mathbf{X}} \otimes \mathcal{S}_{\mathbf{X}} \;,\; \mathcal{T}_{\mathbf{X}} \big) & \text{ by definition, } \end{array}$$

where we used, apart from the above definitions:

1. that internal hom-functors preserve limits

2. the Fubini theorem for ends

3. the co-Yoneda lemma.

This establishes that $[-,-]$ is an internal hom in $Func(\mathbf{X},\mathbf{V})$ for the objectwise tensor product, as claimed.

The natural isomorphisms needed to exhibit the (co)tensoring of $\mathbf{C}^{\mathbf{X}}$ both follow essentially the same sequence of steps, just up to the relevant substitutions. For definiteness we spell it out again, but now proceeding in the reverse order of steps:

Given

• $\mathcal{S}_{\mathbf{X}} \in Func(\mathbf{X},\mathbf{V})$,

• $\mathscr{V}_{\mathbf{X}},\, \mathscr{W}_{\mathbf{X}} \in Func(\mathbf{X},\mathbf{V})$,

• $x \in \mathbf{X}$,

consider the following sequence of $V$-enriched natural isomorphisms in these variables:

Starting with

$$\begin{array}{ll} \mathbf{C}^{\mathbf{X}} \big( \mathcal{S}_{\mathbf{X}} \cdot \mathscr{V}_{\mathbf{X}} \;,\; \mathscr{W}_{\mathbf{X}} \big)_x \\ \;\simeq\; \int_{z \in \mathbf{X}} \mathbf{C}\Big( \mathbf{X}(x,z) \cdot \big( \mathcal{S}_{\mathbf{X}} \cdot \mathscr{V}_{\mathbf{X}} \big)_{z} ,\, \mathscr{W}_{z} \Big) & \text{ by definition } \\ \;\simeq\; \int_{z \in \mathbf{X}} \mathbf{C}\big( \mathbf{X}(x,z) \cdot \mathcal{S}_{z} \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \big) & \text{ by definition } \\ \;\simeq\; \cdots \end{array}$$

we invoke the co-Yoneda lemma, either to introduce a fresh variable on $\mathbf{X}(x,-) \cdot \mathcal{S}_{(-)}$

$$\begin{array}{ll} \cdots \\ \;\simeq\; \int_{z \in \mathbf{X}} \mathbf{C}\Big( \int^{y \in \mathbf{X}} \mathbf{X}(y,z) \cdot \big( \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \big) \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \Big) & \text{ co-Yoneda lemma } \\ \;\simeq\; \int_{z \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{C}\Big( \mathbf{X}(y,z) \cdot \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \Big) & \text{ enriched homs preserve enriched limits } \\ \;\simeq\; \int_{z \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{V} \Big( \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \;,\; \mathbf{C}\big( \mathbf{X}(y,z) \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \big) \Big) & \text{ tensoring iso of }\; \mathbf{C} \\ \;\simeq\; \int_{y \in \mathbf{X}} \int_{z \in \mathbf{X}} \mathbf{V} \Big( \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \;,\; \mathbf{C}\big( \mathbf{X}(y,z) \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \big) \Big) & \text{ Fubini theorem for ends } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{V} \Big( \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \;,\; \int_{z \in \mathbf{X}} \mathbf{C}\big( \mathbf{X}(y,z) \cdot \mathscr{V}_{z} \;,\; \mathscr{W}_{z} \big) \Big) & \text{ enriched homs preserve enriched limits } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{V}\Big( \mathbf{X}(x,y) \cdot \mathcal{S}_{y} \;,\; \mathbf{C}^{\mathbf{X}} \big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big)_y \Big) & \text{ definition } \\ \;\simeq\; \mathbf{V}^{\mathbf{X}}\Big( \mathcal{S}_{\mathbf{X}} \;,\; \mathbf{C}^{\mathbf{X}} \big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big) \Big)_x & \text{ definition } \end{array}$$

or to get a fresh variable on $\mathbf{X}(x,-) \cdot \mathscr{V}_{(-)}$:

$$\begin{array}{ll} \cdots \\ \;\simeq\; \int_{z \in \mathbf{X}} \mathbf{C} \Big( \mathcal{S}_z \cdot \int^{y \in \mathbf{X}} \mathbf{X}(y,z) \cdot \big( \mathbf{X}(x,y) \cdot \mathcal{V}_{y} \big) \;,\; \mathscr{W}_{z} \Big) & \text{ co-Yoneda lemma } \\ \;\simeq\; \int_{z \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{C} \Big( \mathbf{X}(x,y) \cdot \mathbf{X}(y,z) \cdot \mathcal{S}_z \cdot \mathcal{V}_{y} \;,\; \mathscr{W}_{z} \Big) & \text{ enriched homs preserve enriched limits } \\ \;\simeq\; \int_{z \in \mathbf{X}} \int_{y \in \mathbf{X}} \mathbf{C} \Big( \mathbf{X}(x,y) \cdot \mathcal{V}_{y} \;,\; \big(\mathscr{W}_{z}\big)^{ \mathbf{X}(y,z) \cdot \mathcal{S}_z } \Big) & \text{ cotensoring iso of }\; \mathbf{C} \\ \;\simeq\; \int_{y \in \mathbf{X}} \int_{z \in \mathbf{X}} \mathbf{C} \Big( \mathbf{X}(x,y) \cdot \mathcal{V}_{y} \;,\; \big(\mathscr{W}_{z}\big)^{ \mathbf{X}(y,z) \cdot \mathcal{S}_z } \Big) & \text{ Fubini theorem for ends } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{C} \Big( \mathbf{X}(x,y) \cdot \mathcal{V}_{y} \;,\; \int_{z \in \mathbf{X}} \big(\mathscr{W}_{z}\big)^{ \mathbf{X}(y,z) \cdot \mathcal{S}_z } \Big) & \text{ enriched homs preserve enriched limits } \\ \;\simeq\; \int_{y \in \mathbf{X}} \mathbf{C} \bigg( \mathbf{X}(x,y) \cdot \mathcal{V}_{y} \;,\; \Big( \big( \mathscr{W}_{\mathbf{X}} \big)^{ \mathcal{S}_{\mathbf{X}} } \Big)_y \bigg) & \text{ definition } \\ \;\simeq\; \mathbf{C}^{\mathbf{X}} \Big( \mathcal{V}_{\mathbf{X}} \;,\; \big(\mathscr{W}_{\mathbf{X}}\big)^{ \mathcal{S}_{\mathbf{X}} } \Big)_x & \text{ definition } \end{array}$$

By naturality in $x \in \mathbf{X}$, these constitute the required $\mathbf{V}^{\mathbf{X}}$--enriched natural isomorphisms for exhibiting the claimed (co)tensoring:

$$\mathbf{C}^{\mathbf{X}} \big( \mathcal{S}_{\mathbf{X}} \cdot \mathscr{V}_{\mathbf{X}} \;,\; \mathscr{W}_{\mathbf{X}} \big) \;\simeq\; \mathbf{V}^{\mathbf{X}} \Big( \mathcal{S}_{\mathbf{X}} \;,\; \mathbf{C}^{\mathbf{X}}\big( \mathscr{V}_{\mathbf{X}} \;,\; \mathscr{W}_{\mathbf{X}} \big) \Big) \;\simeq\; \mathbf{C}^{\mathbf{X}} \Big( \mathscr{V}_{\mathbf{X}} \;,\; \big(\mathscr{W}_{\mathbf{X}}\big)^{ \mathcal{S}_{\mathbf{X}} } \Big) \,.$$

From this, finally, follows an $\mathbf{V}^{\mathbf{X}}$-enriched composition operation

$$\mathbf{C}^{\mathbf{X}}\big( \mathscr{R}_{\mathbf{X}} ,\, \mathscr{V}_{\mathbf{X}} \big) \otimes \mathbf{C}^{\mathbf{X}}\big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big) \longrightarrow \mathbf{C}^{\mathbf{X}}\big( \mathscr{R}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big)$$

to be defined as the adjunct (via the just established adjunctions) of the consecutive evaluation maps (being themselves the respective adjunction counits):

$$\mathscr{R}_{\mathbf{X}} \cdot \mathbf{C}^{\mathbf{X}}\big( \mathscr{R}_{\mathbf{X}} ,\, \mathscr{V}_{\mathbf{X}} \big) \cdot \mathbf{C}^{\mathbf{X}}\big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big) \overset{ev}{\longrightarrow} \mathscr{V}_{\mathbf{X}} \cdot \mathbf{C}^{\mathbf{X}}\big( \mathscr{V}_{\mathbf{X}} ,\, \mathscr{W}_{\mathbf{X}} \big) \overset{ev}{\longrightarrow} \mathscr{W}_{\mathbf{X}} \,.$$

Related concepts

• enriched Reedy category

• model structure on homotopical presheaves

• model structure on sSet-presheaves

References

An original article:

• Brian Day, Max Kelly, Enriched functor categories, in: Reports of the Midwest Category Seminar III, Lecture Notes in Mathematics 106 (1969) 178-191 [doi:10.1007/BFb0059146, pdf]

Review includes

• Brian Day, On closed categories of functors, Reports of the Midwest Category Seminar IV, Lecture Notes in Mathematics Vol. 137. Springer-Verlag, 1970, pp 1-38 (pdf)

• Max Kelly, section 2.2 p. 29 of Basic concepts of enriched category theory (pdf)