  The problem of routing in graphs using node-disjoint paths has received a lot
of attention and a polylogarithmic approximation algorithm with constant
congestion is known for undirected graphs [Chuzhoy and Li 2016] and [Chekuri
and Ene 2013]. However, the problem is hard to approximate within polynomial
factors on directed graphs, for any constant congestion [Chuzhoy, Kim and Li
2016].
  Recently, [Chekuri, Ene and Pilipczuk 2016] have obtained a polylogarithmic
approximation with constant congestion on directed planar graphs, for the
special case of symmetric demands. We extend their result by obtaining a
polylogarithmic approximation with constant congestion on arbitrary directed
minor-free graphs, for the case of symmetric demands.
