Section Lifting.
Variable (sig : Type).
Variable (m n : nat).
(* [P] is the premise of the lifted machine [M@I]. *)
Variable (P : @SpecV sig n).
Variable (I : Vector.t (Fin.t n) m). (* [m<=n] *)
Hypothesis (HI : dupfree I).
(* We want to extract from [P] the premise [P'] for [M] *)
Definition Downlift : @SpecV sig m :=
(select I P).
(* Same specification as in [P] on indices not in [I], but as in [Q] for indices in [I] (lifted).  *)
Definition Frame (Q : @SpecV sig m) : @SpecV sig n := fill I P Q.
End Lifting.

Lemma tspec_Downlift_withSpace (m n : nat) (sig : Type) P' (P : SpecV sig n) (I : Vector.t (Fin.t n) m) (ss : Vector.t nat n):
Entails ≃≃( P', Downlift (sig:=sig) (m:=m) (n:=n) (withSpace P ss) I) ≃≃( P',withSpace (Downlift P I) (select I ss)).