Hi Doug: in /course/com3362/sp99/DJ/pure-path I wanted to compute a pure path that is there but DJ and the AP library don't find it. Please can you check. -- Karl // cd A = B C. B = D. C = . D = . No path found for strategy graph: { A -> D bypassing { A, D } } source: { A, D } target: { D, A } java.lang.NullPointerException at Main.main(Main.java:13)