One limitation of the algorithm is that the shortest path consisting of an odd number of arcs will not be detected. Suppose we have a shortest path formula_45 When the depth will reach two hops along the arcs, the forward search will proceed to formula_46 from formula_47, and the backward search will proceed from formula_46 to formula_47. Pictorially, the search frontiers will go through each other, and instead a suboptimal path consisting of an even number of arcs will be returned. This is illustrated in the below diagrams: