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updated mathlib references on monoidal categories
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emilyriehl committed Oct 8, 2024
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5 changes: 4 additions & 1 deletion blueprint/lean_decls
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Expand Up @@ -27,4 +27,7 @@ CategoryTheory.SimplicialCategory.HasCotensors
CategoryTheory.SimplicialCategory.cotensor_bifunctoriality
CategoryTheory.IsSLimit
CategoryTheory.InfinityCosmos
CategoryTheory.LaxMonoidalFunctor
CategoryTheory.LaxMonoidalFunctor
CategoryTheory.instEnrichedCategoryTransportEnrichment
CategoryTheory.categoryForgetEnrichment
CategoryTheory.EnrichedFunctor.forget
13 changes: 9 additions & 4 deletions blueprint/src/content.tex
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Expand Up @@ -831,14 +831,16 @@ \section{Change of base}\label{sec:change-of-base}
\end{center} is finite-product-preserving.
\end{ex}

A finite-product-preserving functor may be used to change the base as follows
A finite-product-preserving functor may be used to change the base as follows:

\begin{proposition}\label{prop:change-of-base}
\uses{defn:lax-monoidal-functor}
\lean{CategoryTheory.instEnrichedCategoryTransportEnrichment}
\leanok
A finite-product-preserving functor $T \colon \cV \to \cW$ between cartesian closed categories induces a change-of-base 2-functor \begin{center} \begin{tikzcd} {\cV}\text{-}\mathcal{C}at \arrow[r, "T_*"] & {\cW}\text{-}\mathcal{C}at\, . \end{tikzcd}\end{center}
\end{proposition}

An early observation along these lines was first stated as \cite[II.6.3]{EilenbergKelly:1966cc}, with the proof left to the reader. We adopt the same tactic and leave the diagram chases to the reader or to \cite[4.2.4]{Cruttwell:2008rr} and instead just give the construction of the change-of-base 2-functor, which is the important thing.
An early observation along these lines was first stated as \cite[II.6.3]{EilenbergKelly:1966cc}, with the proof left to the reader. We adopt the same tactic and leave the diagram chases to the reader or to \cite[4.2.4]{Cruttwell:2008rr} and instead just give the construction of the change-of-base 2-functor, which is the important thing. The construction of a $\cW$-category $T_*\cC$ from a $\cV$-category $\cC$ exists in Mathlib in the more general setting of a lax monoidal functor $T$, but change of base for enriched functors or natural transformations has not been formalized.

\begin{proof} Let $\cC$ be a $\cV$-category and define a $\cW$-category $T_*\cC$ to have the same objects and to have mapping objects $T_*\cC(x,y) \coloneq T\cC(x,y)$. The composition and identity maps are given by the composites
\begin{center}
Expand Down Expand Up @@ -888,10 +890,13 @@ \section{Change of base}\label{sec:change-of-base}
As a special case:

\begin{corollary}\label{cor:free-underlying-2-adj}
\uses{prop:change-of-base-adjunction} For any cartesian closed category $\cV$ with coproducts, the underlying category construction and free category construction define adjoint 2-functors
\uses{prop:change-of-base-adjunction}
\lean{CategoryTheory.categoryForgetEnrichment}
\lean{CategoryTheory.EnrichedFunctor.forget}
\leanok For any cartesian closed category $\cV$ with coproducts, the underlying category construction and free category construction define adjoint 2-functors
\begin{center}
\begin{tikzcd}[column sep=large]
\Cat \arrow[r, bend left=20, hook, start anchor=10, end anchor=170] \arrow[r, phantom, "\bot"] & \eCat{\cV} \arrow[l, bend left=20, start anchor=190, end anchor=-10, "(-)_0"]
\mathcal{C}at \arrow[r, bend left=20, hook, start anchor=10, end anchor=170] \arrow[r, phantom, "\bot"] & {\cV}\text{-}\mathcal{C}at \arrow[l, bend left=20, start anchor=190, end anchor=-10, "(-)_0"]
\end{tikzcd}
\end{center}
\end{corollary}
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