Pfaff's problem and its generalizations, J.A. Schouten and W. v.d. Kulk. Schouten, J. A. (Jan Arnoldus), 1883- Kulk, W. van der (Wouter), joint author. Pfaff's problem. QA381 .S38 517.38 SCP Bibliography: p. [534]-536. Oxford : Clarendon Press, 1949. 1949. 1949 Text xvi, 542 p. ; eng