```
% 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" , "" )
    ]
]
```