fact: Fixpoint mapi' (n : nat) {A B} (f : nat -> A -> t B) (l: mlist A) : t (mlist B) := match l with | [m:] => ret [m:] | x :m: xs => mcons <$> f n x <*> mapi' (S n) f xs end.
imports: Strings.String NArith.BinNat Mtac2(Logic Datatypes Logic List Utils MTele Pattern Specif)