# Math

### Custom configuration, and inject JavaScript in posts

Motivation To enable TikZ in my note, I add a header in layout/partial/header.html at first. But this change injects the javascript lines into all my posts which don’t need to include the TikZ. So I want to inject JavaScript in case that I mark the post as “TikZ enabled”. How to Create a HTML template In layouts/partials/header.html. {{ if and .IsPage (eq (.Param "tikz") true) }} <link rel="stylesheet" type="text/css" href="https://tikzjax.com/v1/fonts.css"> <script src="https://tikzjax.

### Category Theory (Apr.2021. updating continuously)

Materials Category Theory by Steve Awodey Very kind “Category Theory For Beginners” by Richard Southwell. Definition of a category Objects and arrows are there. There should be identity arrows. Arrows should be composited. Associativity holds. Terminology: domain and codomain $\mathrm{dom}(f)\xrightarrow{f} \mathrm{cod}(f)$ Functor A Functor is a mapping between categories. It’s like an arrow from category to category. It preseves compositions $F(g\cdot f) = F(g)\cdot F(f)$. Identitiy arrows are mapped to identity arrows.