Let D be an integer at least 3 and let H(D, 2) denote the hypercube. It is known that H(D, 2) is a Q-polynomial distance-regular graph with diameter D, and its eigenvalue sequence and its dual eigenvalue sequence are all {D-2i}D i=0. Suppose that denotes the tetrahedron algebra. In this paper, the authors display an action of ■ on the standard module V of H(D, 2). To describe this action, the authors define six matrices in Mat X(C), called A, A*, B, B*, K, K*.Moreover, for each matrix above, the authors compute the transpose and then compute the transpose of each generator of ■ on V.
Let A be a finite-dimensional algebra over an algebraically closed field k,E the category of all exact sequences in A-mod,MP(respectively,MI)the full subcategory of E consisting of those objects with projective(respectively,injective)middle terms.It is proved that MP(respectively,MI)is contravariantly finite(respectively,covariantly finite)in E.As an application,it is shown that MP=MI is functorially finite and has Auslander-Reiten sequences provided A is selfinjective.
