文摘
Bichain graphs form a bipartite analog of split permutation graphs, also known as split graphs of Dilworth number 2. Unlike graphs of Dilworth number 1 that enjoy many nice properties, split permutation graphs are substantially more complex. To better understand the global structure of split permutation graphs, in the present paper we study their bipartite analog. We show that bichain graphs admit a simple geometric representation and have a universal element of quadratic order, i.e. an X14003837&_mathId=si1069.gif&_user=111111111&_pii=S0166218X14003837&_rdoc=1&_issn=0166218X&md5=45a91d949d2524806f3fbbcf32838c18" title="Click to view the MathML source">n-universal bichain graph with 14289741b5ace10dc817" title="Click to view the MathML source">n2 vertices. The latter result improves a recent cubic construction of universal split permutation graphs.