unprefixed :: Eq a => [a] -> [a] -> Maybe [a]
unprefixed prefix full
  | prefix `isPrefixOf` full = Just $ drop (length prefix) full
  | otherwise = Nothing
unprefixed :: Eq a => [a] -> [a] -> Maybe [a]
unprefixed prefix full
  | prefix `isPrefixOf` full = Just $ drop (length prefix) full
  | otherwise = Nothing
unprefixed prefix full
  | prefix `isPrefixOf` full = Just $ drop (length prefix) full
  | otherwise = Nothing