kramdown turns any line containing a pipe into a table; GitHub's renderer does not

Fact

Jekyll's default Markdown processor is kramdown, whose table syntax needs no |---| delimiter row: one line containing | characters is a complete one-row table. GFM — what GitHub.com renders repository Markdown with — requires the delimiter row, so the same line is ordinary prose there.

A sentence such as Tangency turns into $|a|=|b|=r$, so … therefore reads correctly in the repository and is rebuilt as a five-cell table on the GitHub Pages site generated from that identical file.

Why it matters

The corruption is silent and content-dependent: the build succeeds, most pages are fine, and only the lines that happen to contain a pipe are wrong — so it surfaces as "this one page looks broken" long after the setup was verified. Pipes are common in prose about absolute values, norms, P(A|B), set-builder notation, divisibility, and shell pipelines.

How to apply

Render the site with the processor GitHub itself uses, rather than escaping pipes by hand forever:

markdown: CommonMarkGhPages
commonmark:
  options: [SMART, FOOTNOTES, UNSAFE]
  extensions: [strikethrough, autolink, table, tagfilter]

jekyll-commonmark-ghpages ships with the github-pages gem, so no plugin declaration is needed. Note the knock-on effect on math: kramdown rewrites display $$…$$ to \[…\] while CommonMark leaves it alone, so configure MathJax for both delimiter pairs.