def backtrack_shortest_common_supersequences(sequences, upperbound=None):
    """ backtrack with pruning, then filter out the shortest SCSs (they are not unique!)"""
    if not upperbound:
        upperbound = 10000000
    result = backtrack_scs(sequences, [], upperbound)
    return [x for x in result if len(x) == min([len(y) for y in result])]
 backtrack with pruning, then filter out the shortest SCSs (they are not unique!)
recipes/Python/578678_Shortest_CommSupersequence/recipe-578678.py