With the rapid growth of integration scale of VLSI chips and the present need for reliable computers in space exploration, fault diagnosis and fault toleran ce have become more important than before, and hence reveal a lot of interest ing topics which attract many researchers to make a great number of contribu tions to this field. In recent years, many new and significant results have been achieved. A quick scan over the proceedings of the conferences on fault tolerant computing and design automation as well as on testing will convince the reader of that. But unfortunately these achievements have not been entire ly reflected in the textbooks, so that there seems to be a gap for the new researcher who already has the basic knowledge and wants to begin research in this area. As a remedy for this deficiency, this book is intended for begin ners, especially graduate students, as a textbook which will lead them to the frontier of some branches of the fault-tolerant computing field. The first chapter introduces the four-valued logic B4 and its applica tions. In 1966 Roth first proposed this four-valued logic as a technique to generate tests for logical circuits, but this work did not concern the mathe matical basis of B4 itself.
