% A regression corpus file for `\def`-family defined-name isolation and the
% `\[`/`\(` shape gate (smoke-test issue #65): stacks-project restyles display
% math by redefining `\[`/`\]` — the control symbol after `\def` is the
% sequence being defined, not a math opener, and the trivlist opens in one
% macro-code body and closes in the other — and passes `\[` to a delimited
% splitter as a data token.
\makeatletter
\def\[{\relax
  \ifmmode\@badmath
  \else
    \begin{trivlist}%
    \item[]\leavevmode
    \hbox to\linewidth\bgroup$\displaystyle
    \hskip\mathindent\bgroup
  \fi}%
\def\]{\relax
  \ifmmode
    \egroup \m@th$\hfil \egroup
    \end{trivlist}%
  \else \@badmath
  \fi}%
\def\@tempa#1$#2#3\@nil{%
  \def\[{#1$#2\def\@currenvir{displaymath}#3}%
}%
\expandafter\@tempa\[\@nil
\makeatother

Real display math still pairs: \[ x + y \] and so does inline \( a \).
