Matrix operators on sequence AkAk

This paper gives necessary or sufficient conditions for a triangular matrix TT to be a bounded operator from AkAk to ArAr, i.e., T∈B(Ak,Ar)T∈B(Ak,Ar) for the case r≥k≥1r≥k≥1 where AkAk is defined by (1.3), and so extends some well-known results.