  M. Laguna and R. Martí. GRASP and path relinking for 0-layer straight line crossing minimization. INFORMS Journal on Computing , 00:00-00, 0000. MATH  M. Laguna, J.P. Kelly, J.L. González-Velarde, and F. Glover. Tabu search for multilevel generalized assignment problem. European Journal of Operational Research , 00:000-000, 0000. MATH  E.L. Lawler. Combinatorial optimization: Networks and matroids