-- | typeOf before eval is the same after eval.
prop_typeOf_eval :: Term -> Bool
prop_typeOf_eval t = 
    case eval t of
        Just t' -> typeOf t == typeOf t'
        Nothing -> True


-- | typeOf before eval' is the same after eval'.
prop_typeOf_eval :: Term -> Bool
prop_typeOf_eval t = 
    case eval t of
        Just t' -> typeOf t == typeOf t'
        Nothing -> True


-- | typeOf before eval' is the same after eval'.
prop_typeOf_eval t = 
    case eval t of
        Just t' -> typeOf t == typeOf t'
        Nothing -> True


-- | typeOf before eval' is the same after eval'.