Fix: equation compatible with KateX and GitHub

[FrancoisCapon]

Hi,

With my students we discovered that the former equation is not compatible with GitHub and KateX

GitHub

The following macros are not allowed: operatorname

Katex

auto-render.min.js:1 
 KaTeX auto-render: Failed to parse `
\operatorname{ker} f=\{g\in G:f(g)=e_{H}\}{\mbox{.}}
` with  ParseError: KaTeX parse error: Undefined control sequence: \mbox at position 45: …G:f(g)=e_{H}\}{\̲m̲b̲o̲x̲{.}}

[squidfunk]

Thanks for the PR. So you're proposing another example that works with both, MathJax and KaTeX, do I understand that correctly? Otherwise, I'm not sure why the entire formula was changed 😅

[alexvoss]

Indeed, \mbox is not supported by KaTeX. The proposed formula works in the KaTeX sandbox on their website and on this MathJax sandbox.

[squidfunk]

Alright, let's use this one then.