Definition unop_long (sem: int64 -> int64) (x: aval) :=
  match x with L n => L (sem n) | _ => ntop1 x end.

Lemma unop_long_sound: forall sem v x, vmatch v x -> vmatch (match v with Vlong i => Vlong(sem i) | _ => Vundef end) (unop_long sem x).