General isomorphism problem for one-relator groups
Determine whether the isomorphism problem is decidable for the class of all one-relator groups, i.e., given two finite one-relator presentations, decide algorithmically whether the resulting groups are isomorphic.
References
Finally, in \S(1980) we go further in-depth on some decision problems for one-relator groups, including the conjugacy problem, the isomorphism problem (both of which remain open in general), and the complexity of the word problem.
— The theory of one-relator groups: history and recent progress
(2501.18306 - Linton et al., 30 Jan 2025) in Section 8, Decision problems (1960–1980)