Give an example of a directed graph G = (V, E), a source vertex s ∈ V, and a set of tree edges E_π ⊆ E such that for each vertex ν ∈ V, the unique simple path in the graph (V, E_π) from s to ν is a shortest path in G, yet the set of edges E_π cannot be produced by running BFS on G, no matter how the vertices are ordered in each adjacency list.