D.H. Sattinger ; with an appendix by P. Olver. Benedict H. Gross ; with an appendix by B. Mazur. Dale Husemèoller ; with an appendix by Ruth Lawrence. Pierre H. Bérard ; with an appendix by G. Besson. Serge Lang ; [with an appendix by Karl Rubin]. Matthias Kreck ; with an appendix by Neal W. Stoltzfus.