Groups with ALOGTIME-hard word problems and PSPACE-complete compressed word problems

09/30/2019

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by   Laurent Bartholdi, et al.

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We give lower bounds on the complexity of the word problem of certain non-solvable groups: for a large class of non-solvable infinite groups, including in particular free groups, Grigorchuk's group and Thompson's groups, we prove that their word problem is NC^1-hard. For some of these groups (including Grigorchuk's group and Thompson's groups) we prove that the compressed word problem (which is equivalent to the circuit evaluation problem) is PSPACE-complete.