Complexity of untying \(2\)-knots
Boris Lishak (Sydney)
Embeddings of \(S^2\) into \(S^4\) can be topologically nontrivial. But even if the embedding is trivial, geometrically it can "look" knotted. We will give examples of topologically trivial \(2\)-knots such that their complexity will grow super-exponentially. Complexity will be either defined in terms of Riemannian geometry in the smooth case or combinatorially if the embedding is piece-wise linear. Proofs will use some group theory.