Serge Lang ; [with an appendix by Karl Rubin]. Pierre H. Bérard ; with an appendix by G. Besson. Mario Petrich ; with an appendix by Richard Wiegandt. D.H. Sattinger ; with an appendix by P. Olver. Michael Barr ;with an appendix by Po-Hsiang Chu. Dale Husemèoller ; with an appendix by Ruth Lawrence.