  In this paper a new method for checking the subsumption relation for the
optimal-size sorting network problem is described. The new approach is based on
creating a bipartite graph and modelling the subsumption test as the problem of
enumerating all perfect matchings in this graph. Experiments showed significant
improvements over the previous approaches when considering the number of
subsumption checks and the time needed to find optimal-size sorting networks.
We were able to generate all the complete sets of filters for comparator
networks with 9 channels, confirming that the 25-comparators sorting network is
optimal. The running time was reduced more than 10 times, compared to the
state-of-the-art results.
