答案1
这似乎复制了你的例子:
\documentclass{article}
\usepackage{mathtools,array}
\newenvironment{grammar}[2]
{\begin{tabular}{@{\qquad}>{$}l<{$}@{\qquad}l@{}}
\multicolumn{1}{@{}l@{}}{$#1$}&\multicolumn{1}{l@{}}{\hspace{-2em}#2}\\}
{\end{tabular}}
\begin{document}
\begin{grammar}{P,Q,R\Coloneqq}{processes (or plain processes)}
\mathbf{0} & null process \\
P\mid Q & parallel composition \\
!P & replication \\
\nu n.P & name restriction (``new'') \\
\text{if $M=N$ then $P$ else $Q$} & conditional \\
u(x).P & message input \\
\bar{u}(N).P & message output
\end{grammar}
\end{document}