lastCommonList (f1:t1) (f2:t2) last'
  | f1 == f2  = lastCommonList t1 t2 f1
  | otherwise = last'
lastCommonList (f1:t1) (f2:t2) last'
  | f1 == f2  = lastCommonList t1 t2 f1
  | otherwise = last'
lastCommonList (f1:t1) (f2:t2) last'
  | f1 == f2  = lastCommonList t1 t2 f1
  | otherwise = last'