Conjectural standard homomorphism families from dihedral type to type D

Let nn be in the congruence classes specified below, let K1,K2[0,n]K_1,K_2\subset[0,n], and let w0Sw_0^S denote the longest element of the parabolic subgroup indexed by SS. For i{1,2}i\in\{1,2\}, define the displayed images by deleting from KiK_i the indicated arithmetic progression.

Type-D family conjecture. The following assignments define standard homomorphisms:

  1. From Br+(I2(n+1))\operatorname{Br}^+(I_2(n+1)) to Br+(Dn+1)\operatorname{Br}^+(D_{n+1}),
T^iTw0Ki(2i+4Z0),i{1,2},\widehat T_i\mapsto T_{w_0^{K_i\setminus(2i+4\mathbb Z_{\ge0})}},\qquad i\in\{1,2\},

for (K1,K2)(K_1,K_2) equal to ([1,n],{0}[2,n2])([1,n],\{0\}\cup[2,n-2]) when n1+4Z>0n\in1+4\mathbb Z_{>0}, ([1,n],{0}[2,n])([1,n],\{0\}\cup[2,n]) when n1+2Z>0n\in1+2\mathbb Z_{>0}, or ([1,n2],{0}[2,n])([1,n-2],\{0\}\cup[2,n]) when n3+4Z0n\in3+4\mathbb Z_{\ge0}.

  1. From Br+(I2(2n))\operatorname{Br}^+(I_2(2n)) to Br+(Dn+1)\operatorname{Br}^+(D_{n+1}),
T^iTw0Ki(2i1+4Z0),i{1,2},\widehat T_i\mapsto T_{w_0^{K_i\setminus(2i-1+4\mathbb Z_{\ge0})}},\qquad i\in\{1,2\},

for (K1,K2)(K_1,K_2) equal to ([0,n],{1}[4,n2])([0,n],\{1\}\cup[4,n-2]) when n4Z>0n\in4\mathbb Z_{>0}, ([0,n],{1}[4,n])([0,n],\{1\}\cup[4,n]) when n2Z>1n\in2\mathbb Z_{>1}, or ([0,n2],{1}[4,n])([0,n-2],\{1\}\cup[4,n]) when n2+4Z>0n\in2+4\mathbb Z_{>0}.

The paper presents these as conjectural families of standard homomorphisms into type DD, following the conjectural type-AA and type-BB families.

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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