The paper is quite old, Num is no longer a subclass of Eq: ghci> :i Num class Num a where (+) :: a -> a -> a thus ‘memsq’ would look as follows:

The paper is quite old, Num is no longer a subclass of Eq: ghci> :i Num class Num a where (+) :: a -> a -> a thus ‘memsq’ would look as follows: memsq :: (Eq a, Num a) => [a] -> a -> Bool memsq xs x = square x `elem` xs