Jérôme Monnot Vangelis Th. Paschos Sophie Toulouse Differential approximation results for the traveling salesman problem with distances 1 and 2. 557-568 2003 145 European Journal of Operational Research 3 http://dx.doi.org/10.1016/S0377-2217(02)00222-9 db/journals/eor/eor145.html#MonnotPT03