Before revision:  We also discuss the hardness of the problem , achieving a better lower bound than the previous one [ IPL 2019 ] . We believe our simplified method of analysis can be helpful to deal with similar problems on general undirected graphs .
After revision:  We also discuss the hardness of the problem , achieving a better lower bound than the previous one [ IPL 2019 ] -hard w.r.t.\ parameter k-c. We also consider the problem on acyclic planar graphs, but this time we restrict ourselves to the edge-disjoint shortest paths problem. We show that even on acyclic planar graphs there is no f(k)n^{o(k) .