This is the second volume of a series of books in various aspects of Mathematical Physics. Mathematical Physics has made great strides in recent years, and is rapidly becoming an important dis- cipline in its own right. The fact that physical ideas can help create new mathematical theories, and rigorous mathematical theo- rems can help to push the limits of physical theories and solve problems is generally acknowledged. We believe that continuous con- tacts between mathematicians and physicists and the resulting dialogue and the cross fertilization of ideas is a good thing. This series of...