어느 책 서문 중:Many mathematical monographs of today start with two claims. One is to be self-contained. This book is not self-contained by the nature of its topic. The other claim is to be usable for graduate students. It has been my experience that usually, this must be taken with caution and is mostly true only in the presence of a guiding hand that is acquainted with the topic. I think that this is true here as well.

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