Definition unop_float (sem: float -> float) (x: aval) :=
match x with F n => F (sem n) | _ => ntop1 x end.

Lemma unop_float_sound:
forall sem v x,
vmatch v x ->
vmatch (match v with Vfloat i => Vfloat(sem i) | _ => Vundef end) (unop_float sem x).