Definition unop_single (sem: float32 -> float32) (x: aval) :=
match x with FS n => FS (sem n) | _ => ntop1 x end.

Lemma unop_single_sound:
forall sem v x,
vmatch v x ->
vmatch (match v with Vsingle i => Vsingle(sem i) | _ => Vundef end) (unop_single sem x).