Complexity classification of the graph isomorphism problem
Determine whether the graph isomorphism decision problem is NP-complete or solvable in polynomial time.
References
The first problem is the graph isomorphism problem, which asks one to decide for two given graphs $G$ and $H$ whether they are isomorphic. This problem is a classical example of a problem for which it is not known whether it is NP-complete or solvable in polynomial time.
                — Computer-assisted graph theory: a survey
                
                (2508.20825 - Jooken, 28 Aug 2025) in Section 2.2 (Underlying principles), first bullet on the graph isomorphism problem