$q$-Inverting pairs of linear transformations and the $q$-tetrahedron   algebra
  As part of our study of the $q$-tetrahedron algebra $\boxtimes_q$ we introduce the notion of a $q$-inverting pair. Roughly speaking, this is a pair of invertible semisimple linear transformations on a finite-dimensional vector space, each of which acts on the eigenspaces of the other according to a certain rule. Our main result is a bijection between the following two sets:   (i) the isomorphism classes of finite-dimensional irreducible $\boxtimes_q$-modules of type 1;   (ii) the isomorphism classes of $q$-inverting pairs. 
Tatsuro Ito and Paul Terwilliger