isInfixOf :: (Eq a) => [a] -> [a] -> Bool
isInfixOf needle haystack = any (isPrefixOf needle) (tails haystack)
--- | The 'nub' function removes duplicate elements from a list.
+-- | /O(n^2)/. The 'nub' function removes duplicate elements from a list.
-- In particular, it keeps only the first occurrence of each element.
-- (The name 'nub' means \`essence\'.)
-- It is a special case of 'nubBy', which allows the programmer to supply