Remark in_remove:
  forall (A: Type) (eq: forall (x y: A), {x=y}+{x<>y}) x y l,
  In y (List.remove eq x l) <-> x <> y /\ In y l.

Lemma symbols_preserved: forall (s: ident), Genv.find_symbol tge s = Genv.find_symbol ge s.