Cases

Under pic math the \cases becomes a picture due to the \left and \right operations.

<..plain,latex math..>+
 \NewConfigure{cases}[8]{\c:def\a:cases{#1}\c:def\b:cases{#2}%
     \c:def\c:cases{#5}\c:def\d:cases{#6}\c:def\e:cases{#7}%
     \c:def\f:cases{#8}\c:def\g:cases{#3}\c:def\h:cases{#4}}
 \Configure{cases}{}{}{}{}{}{}{}{}
 -_-_-

<..plain,latex math..>+
 \def\:tempc#1{\tx:halign{cases}{#1}}
 \HLet\cases=\:tempc
                                     \catcode‘\#13 \catcode‘\!6
 \def\reg:cases!1{\left\{\vcenter{\normalbaselines\m@th  \g:cases
    \SaveMkHalignConf:g{cases}\RecallTeXcr
    \MkHalign#{$#$&{#}}!1\crcr
    \EndMkHalign\RecallMkHalignConfig   \h:cases}\right.}
                                     \catcode‘\#=6 \catcode‘\!=12
 -_-_-