The entire text has been restructured, rewritten and updated to cater to the revised syllabi of almost all universities, and various other professional examinations. During the course of rewriting, it has been specially borne in mind to retain all the basic features of the previous editions especially the simplicity of presentation, lucidity of style and analytical approach which have been appreciated by the readers throughout the country. A conscious effort has been made to make the presentation of all topics discussed very simple and to develop the subject-matter in such step-by-step manner that the book can serve as self-study text for the students. A number of typical problems have been added as solved examples in each chapter. These will enable the reader to have a better and thoughtful understanding of the basic concepts of the theory and its various applications. Several new topics have been added at appropriate places in various chapters to make the treatment of subject matter more exhaustive and up-to-date.