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Complexity classification of the graph isomorphism problem

Determine whether the graph isomorphism decision problem is NP-complete or solvable in polynomial time.

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Background

Graph isomorphism sits at the core of avoiding duplication in generation and underlies canonical labeling and automorphism computations. Despite extensive paper and major algorithmic advances, the precise complexity-theoretic status of GI—NP-complete versus polynomial-time solvable—remains unresolved.

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