When is hyponormality for 2-variable weighted shifts invariant under powers?

Raul Curto, Jasang Yoon

For 2-variable weighted shifts W_{(α,β)}(T_1, T_2) we study the invariance of (joint) k- hyponormality under the action (h,\ell) -> W_{(α,β)}^{(h,\ell)}(T_1, T_2):=(T_1^k,T_2^{\ell…