Patrick Dehornoy (Université de Caen)

Wednesday 29th March, 3.30-4.30pm, Carslaw 535 (Faculty Meeting Room) -- note unusual day, time, and room

The word reversing method for presented (semi)groups

Word reversing is a general syntactical procedure that can be used for each semigroup presentation. In good cases, it allows one to easily decide some properties of the associated semigroup or group, like cancellativity, existence of lower common multiples, decidability of the word problem, Garsideness, existence of a cubical resolution. The nice point is that there exists an effective criterion for recognizing which cases are good in the sense above, and even a completion process that possibly turns an initially bad presentation into a good one. This approach is closely related with the chainability approach, but it seems to apply to more cases.