Hint Resolve check_cast_sound check_bool_sound: ty.

Lemma type_combine_cast:
forall t1 t2 t,
type_combine t1 t2 = OK t ->
match t1 with Tarray _ _ _ => False | Tfunction _ _ _ => False | _ => True end ->
match t2 with Tarray _ _ _ => False | Tfunction _ _ _ => False | _ => True end ->
wt_cast t1 t /\ wt_cast t2 t.