fact: Definition find {A} (b : A -> t bool) : mlist A -> t (moption A) := fix f l := match l with | [m:] => ret mNone | x :m: xs => mif b x then ret (mSome x) else f xs end.
imports: Strings.String NArith.BinNat Mtac2(Logic Datatypes Logic List Utils MTele Pattern Specif)