Shortest paths between shortest paths

We study the following problem on recon guring shortest paths in graphs: Given two shortest st paths, what is the minimum number of steps required to transform one into the other, where each intermediate path must also be a shortest s-t path and must di er from the previous one by only one vertex. We prove that the shortest recon guration sequence can be exponential in the size of the graph and that it is NP-hard to compute the shortest recon guration sequence even when we know that the sequence has polynomial length.