The codimension-two spin-genus representation conjecture for quadratic forms

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Let q:Zm→Zq:\mathbb{Z}^m\to\mathbb{Z} and Q:Zn→ZQ:\mathbb{Z}^n\to\mathbb{Z} be integral quadratic forms with m<nm<n, and let

min⁡(q):=min⁡x∈Zm∖{0}q(x).\min(q):=\min_{x\in\mathbb{Z}^m\setminus\{0\}}q(x).

Assume that qq is primitively represented by an element of the spin genus of QQ, and that n−m=2n-m=2. Codimension-two spin-genus representation conjecture. There exists a constant C(Q)>0C(Q)>0 such that

min⁡(q)≥C(Q)\min(q)\geq C(Q)

implies that qq is primitively represented by QQ. The local representation and minimum conditions are insufficient in codimension two because of spinor obstructions; the conjecture addresses whether the spin-genus condition becomes sufficient for sufficiently large minimum. Its m=1m=1 case, concerning primitive representations of integers, has been established by Duke and Schulze-Pillot using estimates for Fourier coefficients of half-integral-weight forms, so the general statement is resolved only in that special case.

References

Primary source

Wooyeon Kim, Andreas Wieser and Pengyu Yang, “Representations of binary quadratic forms by quaternary quadratic forms”, arXiv:2604.19437 (2026).

Additional references

2 papers in this index state this conjecture (2025–2026). The statement above is taken from the most recent of them; the others are arXiv:2511.22877.

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