Disjoint paths in a planar graph : a general theorem / G. Ding, A. Schrijver, P.D. SeymourA simpler proof and a generalization of the zero-trees theorem / A. Schrijver, P.D. SeymourDisjoint cycles in directed graphs on the torus and the Klein bottle / G. Ding, A. Schrijver, P.D. SeymourPacking odd paths / A. Schrijver, P.D. Seymour