gives a maximal set of non-adjacent edges between the two vertex sets of the bipartite graph.
The bipartite graph represented by an matrix consists of the row and column vertex sets and C, with a vertex iR and jC connected if the matrix element .
The bipartite graph represented by a rule list consists of vertex sets R=Union[{i1, i2, ...}] and C=Union[{j1, j2, ...}], with a vertex iR and jC connected if the rule is included in the rule list.
returns a list of index pairs where the number of pairs k is not larger than either vertex set.