The stable set polytope of ($P_6$,triangle)-free graphs and new facet-inducing graphs

The stable set polytope of a graph $G$, denoted as STAB($G$), is the convex hull of all the incidence vectors of stable sets of $G$. To describe a linear system which defines STAB($G$) seems to be a difficult task in the general case. In this paper we present a complete description of the stable set polytope of ($P_6$,triangle)-free graphs (and more generally of ($P_6$,paw)-free graphs). For that we combine different tools, in the context of a well known result of Chv'atal \cite{Chvatal1975} which allows to focus just on prime facet-inducing graphs, with particular reference to a structure result on prime ($P_6$,triangle)-free graphs due to Brandst"adt et al. \cite{BraKleMah2005}. Also we point out some peculiarities of new facet-inducing graphs detected along this study with the help of a software.