Definition prog_var_block (rho: environ) (il: list ident) (b: block) : Prop :=
  Exists (fun id => match ge_of rho id with Some b' => b'=b | _ => False end) il.

Lemma Pos_to_nat_eq_S: forall b, Pos.to_nat b = S (nat_of_Z (Z.pos b) - 1).