Sunil Chopra Giovanni Rinaldi The Graphical Asymmetric Traveling Salesman Polyhedron: Symmetric Inequalities. 602-624 1996 9 SIAM J. Discrete Math. 4 http://epubs.siam.org/sam-bin/dbq/article/22232 db/journals/siamdm/siamdm9.html#ChopraR96