 Alternatively, every graph that requires colors may be formed by combining the Hajós construction, the operation of identifying any two nonadjacent vertices, and the operations of adding a vertex or edge to the given graph, starting from the complete graph .A similar construction may be used for list coloring in place of coloring.For , every -critical graph (that is, every odd cycle) can be generated as a -constructible graph such that all of the graphs formed in its construction are also -critical.