When the first printing of this book sold out in a comparatively short time,
it was decided to reprint the original edition with only small modifications:
I just took the opportunity to correct a handful of minor mistakes and to
provide a few updates to the bibliography. In contrast, the new second edition
has been thoroughly revised, even though the general aims of the book have
remained the same. In particular, I have added some new material, namely
a chapter on the network simplex algorithm and a section on the five color
theorem; this also necessitated some changes in the previous order of the
presentation (so that the numbering differs from that of the first edition,
beginning with Chapter 8). In addition to this, numerous smaller changes
and corrections have been made and several recent developments have been
discussed and referenced. There are also several new exercises