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The Andrews–Curtis Conjecture
open
Posed by James J. Andrews / Martin L. Curtis · 1965 · combinatorial group theory
The problem
A balanced presentation ⟨x₁,…,\(x_{n}\) | r₁,…,\(r_{n}\)⟩ of the trivial group (same number of generators and relators, each a consequence of the others) can always be transformed to ⟨x₁,…,\(x_{n}\) | x₁,…,\(x_{n}\)⟩ by: (1) Nielsen transformations on generators; (2) conjugating a relator; (3) replacing a relator by its product with another.
References
History & significance
Posed in 1965 as a purely group-theoretic question. Akbulut and Kirby (1985) showed it is equivalent to asking whether every contractible 4-manifold built from a 0-handle and 2-handles collapses — connecting it directly to exotic smooth structures in dimension 4 (our smooth-Poincaré entry). Verified computationally for all presentations of length ≤ 12; potential counterexamples (the Miller–Schupp pair) resist all attempts at reduction.
Still open.
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