```
% pandoc -f markdown -t native
\begin{proof}
\newcommand{\x}{\left.\right.}
\x
\end{proof}

1234567890abcdefghi

[\*\a](x)
^D
[RawBlock (Format "tex") "\\begin{proof}\n\\newcommand{\\x}{\\left.\\right.}\n\\left.\\right.\n\\end{proof}"
,Para [Str "1234567890abcdefghi"]
,Para [Link ("",[],[]) [Str "*",RawInline (Format "tex") "\\a"] ("x","")]]
```