Alexander Hulpke (Colorado State University), Rewriting systems and group extensions

Tue, 27 April 2021, 1 pm MDT

The first examples of groups in a textbook are often as words in generators, subject to some easy rules. This seems nice and natural, but gets quickly abandoned once the groups involved become more complicated. A similar disappointment happens when introducing group extensions: Examples in textbooks never go beyond easy cases such as cyclic groups or split extensions. But this is not intended to whine about textbooks. Instead I want to show how a systematic approach to normal form words (namely confluent rewriting systems) can be used to describe group extension (and explicitly compute 2-cohomology), resulting in practically useful (and implemented!) algorithms.