 t1 t2) =
    (if b then parise else id) (prnty' True t1 ++ "->" ++ prnty' False t2)
prnty' b (ArrowT x 
prnty' b (ArrowT "_" t1 t2) =
    (if b then parise else id) (prnty' True t1 ++ "->" ++ prnty' False t2)
prnty' b (ArrowT "_" t1 t2) =
    (if b then parise else id) (prnty' True t1 ++ "->" ++ prnty' False t2)