"""...excellent monograph...This is an invaluable book and an indispensable resource for any serious student of graph theory."" Mathematics of Computing ""...the treatment of topics is clear and self-contained and shows considerable design, work, and thought...as a volume in the series Cambridge Tracts in Mathematics, this book has the mandate to 'take up a single thread in a wide subject and follow its ramifications, thus throwing light on its various aspects.' This book does that, beautifully."" Siam Review"