 Today there is still debate over the ultimate value, or even the correct interpretation, of some of the revisions, revisions that were motivated in large part by the work of some of Russell’s brightest students, including Ludwig Wittgenstein and Frank Ramsey. Appendix B has been notoriously problematic. The appendix purports to show how mathematical induction can be justified without use of the axiom of reducibility; but as Alasdair Urquhart reports,