-- FINISHED


groupCheck :: String -> Bool
groupCheck input =
  let subs = iterate removeSubformula input in
  stableTail subs == ""
groupCheck :: String -> Bool
groupCheck input =
  let subs = iterate removeSubformula input in
  stableTail subs == ""
groupCheck input =
  let subs = iterate removeSubformula input in
  stableTail subs == ""