-- <tuplein t n> is true if <n> is in <t>
tuplein :: Eq a => (a, a) -> a -> Bool
tuplein t n
    | n == fst t    = True
    | n == snd t    = True
    | otherwise     = False
tuplein :: Eq a => (a, a) -> a -> Bool
tuplein t n
    | n == fst t    = True
    | n == snd t    = True
    | otherwise     = False
tuplein t n
    | n == fst t    = True
    | n == snd t    = True
    | otherwise     = False