Without function composition, the category of regularly would have to be ((S\NP)/NP)\((S\NP)/NP), but (crossed) composition allows the ordinary category (S\NP)\(S\NP) to also work in this case.
if the parent (and head) category C is of the form X/$, the algorithm strips off all outermost forward arguments /$ (and syntactic features) from C to obtain C .