Let $P$ be the class of formal languages that have polynomial-time decider, i.e. for each $L\in P$ there exists a Turing-machine $T$ such that for each $w\in L$ machine $T$ decides if $w\in L$ in polynomial time wrt the length of $w$.Is it possible to define a grammar (in any reasonable sense) that could be used to define exactly the languages in $P$? 
A formal grammar for P?
cc.complexity theory;fl.formal languages;grammars