fact: Definition is_head : forall {A : Type} {B : A -> Type} {m:MTele} (uni : Unification) (a : A) (C : MTele_ConstT A m) (success : MTele_sort (MTele_ConstMap (si := Typeₛ) Propₛ (T:=A) (fun a => t (B a)) C)) (failure: t (B a)), t (B a).
imports: Strings.String NArith.BinNat Mtac2(Logic Datatypes Logic List Utils MTele Pattern Specif)