differentiate +pfix and +sfix
::
++ pfix :: discard first rule
~/ %pfix
+ |* sam=*
+ %. sam
(comp |*({a/* b/*} b))
::
++ plug :: first then second
::
++ sfix :: discard second rule
~/ %sfix
+ |* sam=*
+ %. sam
(comp |*({a/* b/*} a))
::
:::: 4f: parsing (rule builders)
