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 hackfun_beyond_block: forall b w w', hackfun w w' -> hackfun (beyond_block b w) (beyond_block b w').