A weighted graph G is called well-covered if all its maximal stable sets have the same weight. G. Let S be a stable set of G (possibly, S = ;). The subgraph G?NS] is called a co-stable subgraph of G. We denote by CSub(G) the set of all co-stable subgraphs of G (considered up to isomorphism). A class of weighted graphs P is called co-hereditary if it is closed under taking co-stable subgraphs, i...

‎in this paper we give a characterization of unmixed tripartite‎ ‎graphs under certain conditions which is a generalization of a‎ ‎result of villarreal on bipartite graphs‎. ‎for bipartite graphs two‎ ‎different characterizations were given by ravindra and villarreal‎. ‎we show that these two characterizations imply each other‎.