diff --git a/category_theory.tex b/category_theory.tex index 3e45a37..533083f 100644 --- a/category_theory.tex +++ b/category_theory.tex @@ -2279,7 +2279,7 @@ \section{Limit and Colimit} \[ \begin{tikzcd}[ampersand replacement=\&] [\mathsf{J},\mathsf{C}]\&[-25pt]\&[+10pt]\&[-30pt]\mathsf{C}\&[-30pt]\&[-30pt] \\ [-15pt] - F \arrow[dd, "\theta"{name=L, left}] + F \arrow[dd, "\theta"{name=L, left}, Rightarrow] \&[-25pt] \& [+10pt] \& [-30pt]\varprojlim F\arrow[dd, "\varprojlim \theta"{name=R}] \\ [-10pt] \& \phantom{.}\arrow[r, "\varprojlim", squigarrow]\&\phantom{.} \& \\[-10pt] @@ -2299,6 +2299,33 @@ \section{Limit and Colimit} \] \end{definition} +\begin{definition}{$\varinjlim$ Functor}{} + Let $\mathsf{J}$ be a small category and $\mathsf{C}$ be a category. If for any functor $F:\mathsf{J}\to\mathsf{C}$, $\varinjlim F$ exists, then we have a functor + \[ + \begin{tikzcd}[ampersand replacement=\&] + [\mathsf{J},\mathsf{C}]\&[-25pt]\&[+10pt]\&[-30pt]\mathsf{C}\&[-30pt]\&[-30pt] \\ [-15pt] + F \arrow[dd, "\theta"{name=L, left}, Rightarrow] + \&[-25pt] \& [+10pt] + \& [-30pt]\varinjlim F\arrow[dd, "\varinjlim \theta"{name=R}] \\ [-10pt] + \& \phantom{.}\arrow[r, "\varinjlim", squigarrow]\&\phantom{.} \& \\[-10pt] + G \& \& \& \varinjlim G + \end{tikzcd} + \] + where $\varinjlim \theta$ is induced by the universal property of $\varinjlim F$ + \[ + \begin{tikzcd}[ampersand replacement=\&, background color=mydefinitbg] + \& \varinjlim F \& \\[+10pt] +F(i) \arrow[ru]\arrow[rr, black!35] \arrow[dd, "\theta_i"'] \& \& F(j) \arrow[lu]\arrow[dd, "\theta_j"] \\[+10pt] + \& \varinjlim G \& \\[+10pt] +G(i) \arrow[ru]\arrow[rr] \& \& G(j)\arrow[lu] + % absulute arrow + \arrow[from=1-2, to=3-2, "\varinjlim \theta"', near end, crossing over] + \end{tikzcd} + \] +\end{definition} + + + \begin{proposition}{Diagonal is Left Adjoint to Limit: $\diagfunctor\dashv \varprojlim$}{} Let $\mathsf{J}$ be a small category and $\mathsf{C}$ be a category. If for any functor $F\in[\mathsf{J},\mathsf{C}]$, $\varprojlim F$ exists, then the functor $\varinjlim:\left[\mathsf{J},\mathsf{C}\right]\to\mathsf{C}$ is right adjoint to the diagonal functor $\diagfunctor:\mathsf{C}\to\left[\mathsf{J},\mathsf{C}\right]$ \[