One often writes formula_11 to denote a bipartite graph whose partition has the parts formula_1 and formula_2, with formula_14 denoting the edges of the graph. If a bipartite graph is not connected, it may have more than one bipartition; in this case, the formula_15 notation is helpful in specifying one particular bipartition that may be of importance in an application. If formula_16, that is, if the two subsets have equal cardinality, then formula_17 is called a "balanced" bipartite graph. If all vertices on the same side of the bipartition have the same degree, then formula_17 is called biregular.