The solution of an open problem on semigroup inclusion classes (Q2665932)

The authors characterize the members of the inclusion class \(\mathbf{I} = [xyxy=xy; \, xyz \in \{xywz, xuyz\}]\) and thereby show that \(\mathbf{I}\) is not covered by \(\mathbf{GRB} = [xyzxy = xy]\) in the lattice of inclusion classes. The reviewer is mystified that the authors define the well-known rectangular bands but not the far from well-known notion of an inclusion class.