One has to give kovod, honor to ones main rebbi (teacher). There are many dinim of how this kovod must be shown. One pertaining to the gemoro in eiruvin is that one must not be in a bath house at the same time because this lowers the "distance" and awe between them (unless the rebbi needs his services there). This din applies all his life even after he has finished studying under him. What happens if he "surpasses" his rebbi and now his rebbi has to study under him? Does he still have to honor his "previous" rebbi?