Alok Aggarwal Don Coppersmith Sanjeev Khanna Rajeev Motwani Baruch Schieber The Angular-Metric Traveling Salesman Problem. 697-711 1999 29 SIAM J. Comput. 3 db/journals/siamcomp/siamcomp29.html#AggarwalCKMS99 http://dx.doi.org/10.1137/S0097539796312721