data Polynomial = Var String                    -- Variables
                | Const Integer                 -- Constant numbers
                | Add Polynomial Polynomial     -- Addition
                | Mul Polynomial Polynomial     -- Multiplication

instance Show Polynomial where
    show (Var x) = show x
    show (Const x) = show x
    show (Add x y) = "(" ++ filter (/= '"') (show x) ++ "+" ++ filter (/= '"') (show x) ++ ")"
    show (Mul x y) = "(" ++ filter (/= '"') (show x) ++ "*" ++ filter (/= '"') (show x) ++ ")"

instance Eq Polynomial where
    (Polynomial x) == (Polynomial y) =