Skip to main content\(\DeclareMathOperator{\homop}{Hom}
\newcommand{\Hom}[2]{\homop\left(#1,\,#2\right)}
\newcommand{\lt}{<}
\newcommand{\gt}{>}
\newcommand{\amp}{&}
\definecolor{fillinmathshade}{gray}{0.9}
\newcommand{\fillinmath}[1]{\mathchoice{\colorbox{fillinmathshade}{$\displaystyle     \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\textstyle        \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptstyle      \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptscriptstyle\phantom{\,#1\,}$}}}
\)
Section 22.2 External links
 If you want to provide a link to a resource outside of your project, you will want the <url> tag. The code
<url href="https://pretextbook.org" visual="pretextbook.org">PreTeXt</url>
produces 
PreTeXt 1 . Note that the footnote is automatically created by the use of 
@visual.