Combinatorics on words

Combinatorics on words
Construction of a Thue-Morse infinite word

Combinatorics on words is a branch of mathematics which applies combinatorics to words and formal languages. The study of combinatorics on words arose independently within several branches of mathematics, e.g. number theory, group theory and probability. It has applications to combinatorial enumeration and fractal analysis and appears in problems of theoretical computer science, automata theory, symbolic dynamics and linguistics. While many applications are new, the classical Chomsky–Schützenberger hierarchy of classes of formal grammars is perhaps the best known result in the field. The development of computerized text and string processing has led to important applications of combinatorics on words. It is involved in the core algorithms for text processing, natural language processing, speech processing and bioinformatics.

The study of combinatorics of words goes back to the works of Axel Thue on nonrepetitive sequences of symbols at the beginning of the 20th century. In the years following there were a few researchers working on words, then major work began in the 1950s when Marcel-Paul Schützenberger studied words in his work on coding theory, and Pyotr Novikov and Sergei Adian studied words in connection with Burnside's problem for groups. The study of combinatorics on words really began to develop rapidly after the publication of Lothaire's book in 1983. Lothaire is a nom de plume of a group of researchers working in this area.

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