1\newenvironment{grammar}
2  {\begingroup
3    \def\orbar{\hbox to 2em{\hfil}$\vert$\hbox to .75em{\hfil}}
4    \def\nobar{\hbox to 2em{\hfil}\phantom{$\vert$}\hbox to .75em{\hfil}}
5    \def\longis{ $\longrightarrow$\hbox to .75em{\hfil}}
6   \penalty-100\vskip 6pt plus 1pt\parindent=0pt\interlinepenalty=5000}
7  {\penalty-200\vskip6pt plus 1pt\endgroup}
8
9\def\bar{$\vert$}
10\def\ang#1{$\langle${\small\rm{}#1}$\rangle$}
11\def\kstar{\raise.5ex\hbox{\scheme{*}}}
12\def\kplus{\raise.5ex\hbox{\scheme{+}}}
13