Injectivity criterion for dihedral standard homomorphisms into type A

Fix n>1n>1, let Brn+1+=Br+(An)\operatorname{Br}^+_{n+1}=\operatorname{Br}^+(A_n), and let σ\sigma be the diagram automorphism with σ(i)=n+1i\sigma(i)=n+1-i for i[1,n]i\in[1,n]. For an interval K[1,n]K\subsetneq[1,n] with K>1|K|>1, let [Φ](1)[\Phi](1) and [Φ](2)[\Phi](2) denote the supports of a homomorphism Φ:Br+(I2(N))Brn+1+\Phi:\operatorname{Br}^+(I_2(N))\to\operatorname{Br}^+_{n+1} as in the converse of the paper's classification theorem; a subset is self-orthogonal in the sense of that theorem.

Dihedral injectivity criterion. Both induced maps Φ\overline\Phi and Φ\overline\Phi_\star are injective if and only if either both [Φ](1)[\Phi](1) and [Φ](2)[\Phi](2) are self-orthogonal, or KK satisfies σ(K)=K\sigma(K)=K.

This criterion is a consequence of the paper's classification of optimal disjoint fully supported standard homomorphisms from dihedral type into type AA. Its status is unclear from the supplied metadata because the parser marked the conjecture environment as unresolved.

Sources & referencesView supporting material

Primary source

Arkady Berenstein, Jacob Greenstein and Jian-Rong Li, “Artin monoids, their homomorphisms and twins”, arXiv:2606.26776 (2026).

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