Weyl equivalence for rank 2 Nichols algebras of diagonal type
  Yetter--Drinfel'd modules of diagonal type admit an equivalence relation which conjecturally preserves dimension and Gel'fand--Kirillov dimension of the corresponding Nichols algebras. This relation is determined explicitly for all rank 2 Yetter--Drinfeld modules where the Gel'fand--Kirillov dimension is known to be finite.   Key Words: Brandt groupoid, Hopf algebra, pseudo-reflections, Weyl group 
I. Heckenberger