Degree-parity conjecture for regular maps from products of spheres

From papers

Let nn and mm be positive integers. A continuous map is considered from the product of spheres Sn×Sm\mathbb{S}^n\times\mathbb{S}^m to Sn+m\mathbb{S}^{n+m}, and (n+mn)\binom{n+m}{n} denotes the corresponding binomial coefficient. Degree-parity conjecture. The following conditions are equivalent:

  1. Every continuous map from Sn×Sm\mathbb{S}^n\times\mathbb{S}^m into Sn+m\mathbb{S}^{n+m} is homotopic to a regular one.
  2. The number (n+mn)\binom{n+m}{n} is odd.

This conjecture extends the equivalence established in the paper for n3n\leq 3 and predicts a complete parity criterion for algebraic approximation of maps from products of spheres. The paper provides new families where the criterion holds, but does not state a resolution in general.

Progress summary

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Sources & referencesView supporting material

Primary source

Juliusz Banecki, “Invariants of real affine varieties based on their complexifications”, arXiv:2605.22941 (2026).

Solutions 0

No solutions have been posted yet.