In this task, you are given two lists A,B. Find the longest common subsequence in the lists A and B.
[991, 1537, 'l', '3809', 'S', '2721', '1877', 's', 'y', 3823], [6893, 'R', 2331, 6457, 4055, '3809', 'S', '2721', '1877', 's', 'H', 'p', 't', 'c']