instance Show Prop where show (Const True) = "T" show (Const False) = "F" show (Var t) = t:[] show (Not p) = " ~" ++ show p show (And p1 p2) = "("++ show p1 ++ " && " ++ show p2 ++ ")" show (Or p1 p2) = "("++ show p1 ++ " || " ++ show p2 ++ ")" show (Imply p1 p2) = show p1 ++ " => " ++ show p2 --------------------------------------------p1,p2,p3 :: Propp1 = And (Var 'A') (Not (Var 'A'))p2 = Or (Var 'A') (Not (Var 'A')) p3 = Imply (Var 'A') (And (Var 'A') (Var 'B'))