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This book is based on notes for a master’s course given at Queen Mary, University
of London, in the 1998/9 session. Such courses in London are quite short, and the
course consisted essentially of the material in the first three chapters, together with
a two-hour lecture on connections with group theory. Chapter 5 is a considerably
expanded version of this.
For the course, the main sources were the books by Hopcroft and Ullman ([20]),
by Cohen ([4]), and by Epstein et al. ([7]). Some use was also made of a later book
by Hopcroft and Ullman ([21]). The ulterior motive in the first three chapters is
to give a rigorous proof that various notions of recursively enumerable language
are equivalent. Three such notions are considered. These are: generated by a type
0 grammar, recognised by a Turing machine (deterministic or not) and defined by
means of a G¨odel numbering, having defined “recursively enumerable” for sets of
natural numbers. It is hoped that this has been achieved without too many arguments
using complicated notation. This is a problem with the entire subject, and it
is important to understand the idea of the proof, which is often quite simple. Two
particular places that are heavy going are the proof at the end of Chapter 1 that a
language recognised by a Turing machine is type 0, and the proof in Chapter 2 that
a Turing machine computable function is partial recursive.
The study of formal languages and automata has proved to be a source of much interest and discussion amongst mathematicians in recent times. This book, written by Professor Ian Chiswell, attempts to provide a comprehensive textbook for undergraduate and postgraduate mathematicians with an interest in this developing field. The first three Chapters give a rigorous proof that various notions of recursively enumerable language are equivalent. Chapter Four covers the context-free languages, whereas Chapter Five clarifies the relationship between LR(k) languages and deterministic (context-free languages). Chiswell's book is unique in that it gives the reader a thorough introduction into the connections between group theory and formal languages. This information, contained within the final chapter, includes work on the Anisimov and Muller-Schupp theorems.
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