subseqs (x:xs) = xss ++ [x] : map (x:) xss
  where xss = subseqs xs
subseqs (x:xs) = xss ++ [x] : map (x:) xss
  where xss = subseqs xs
subseqs (x:xs) = xss ++ [x] : map (x:) xss
  where xss = subseqs xs