Group isomorphism problem
In abstract algebra, the group isomorphism problem is the decision problem of determining whether two given finite group presentations present isomorphic groups.
The isomorphism problem was identified by Max Dehn in 1911 as one of three fundamental decision problems in group theory; the other two being the word problem and the conjugacy problem. All three problems are undecidable: there does not exist a computer algorithm that correctly solves every instance of the isomorphism problem, or of the other two problems, regardless of how much time is allowed for the algorithm to run. In fact the problem of deciding whether a group is trivial is undecidable, a consequence of the Adian-Rabin theorem due to Sergei Adian and Michael O. Rabin.
