addTailNumber (a:as) = do
  (Tail n) <- getObjectAttribute a
  setObjectAttribute (Tail (n + 1)) a
  addTailNumber as
addTailNumber (a:as) = do
  (Tail n) <- getObjectAttribute a
  setObjectAttribute (Tail (n + 1)) a
  addTailNumber as
addTailNumber (a:as) = do
  (Tail n) <- getObjectAttribute a
  setObjectAttribute (Tail (n + 1)) a
  addTailNumber as