文摘
In this paper, we analyze ptolemaic graphs for their properties as chordal graphs. First, two characterizations of ptolemaic graphs are proved. The first one is based on the reduced clique graph, a structure that was defined by Habib and Stacho (Habib and Stacho, 2012). In the second one, we simplify the characterization presented by Uehara and Uno (Uehara and Uno, 2009) with a new proof. Then, known subclasses of ptolemaic graphs are reviewed in terms of minimal vertex separators. We also define another subclass, the laminar chordal graphs, and we show that a hierarchy of ptolemaic graphs can be built based on characteristics of the minimal vertex separators in each subclass.