fact: Definition msig_of_msig2 (A : Type) (P Q : A -> Prop) (X : msig2 P Q) : msig P := mexist P (let (a, _, _) := X in a) (let (x, p, _) as s return (P (let (a, _, _) := s in a)) := X in p).
imports: Notations Datatypes Logic