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 sig_preserved: forall rm f tf, transf_fundef rm f = OK tf -> funsig tf = funsig f.