Solving the word problem in real time

Derek F.\ Holt and Sarah Rees\


word problem, real-time, Dehn algorithm


published in J London Mathematical Society 63 (2001) 623-639


This paper is devoted to the study of groups whose word problem can be solved by a Turing machine which operates in real-time. A recent result of the first author for word hyperbolic groups is extended to prove that under certain conditions the generalised Dehn algorithms of Cannon, Goodman and Shapiro, which clearly run in linear time, can be programmed on real-time Turing machines. It follows that word-hyperbolic groups, finitely generated nilpotent groups and geometrically finite hyperbolic groups all have real-time word problems. \

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