sane_ty :: Category -> Ty -> Bool
sane_ty Compare (TyF t1 (TyF t2 td)) 
   | t1 == t2 && td == TyApp "Bool" []  = True
sane_ty :: Category -> Ty -> Bool
sane_ty Compare (TyF t1 (TyF t2 td)) 
   | t1 == t2 && td == TyApp "Bool" []  = True
sane_ty Compare (TyF t1 (TyF t2 td)) 
   | t1 == t2 && td == TyApp "Bool" []  = True