Definition cast_pointer_to_bool t1 t2 :=
 match t1 with (Tpointer _ _ | Tarray _ _ _ | Tfunction _ _ _) => 
           match t2 with Tint IBool _ _ => true | _ => false end
 | _ => false
end.

Lemma eqb_type_sym: forall a b, eqb_type a b = eqb_type b a.