HACETTEPE JOURNAL OF MATHEMATICS AND STATISTICS, cilt.38, sa.1, ss.51-58, 2009 (SCI-Expanded)
The famous Knopp Core of a single sequence was extended to the P-core of a double sequence by R.F. Patterson. Recently, the MR-core and sigma-core of real bounded double sequences have been introduced and some inequalities analogues to those for Knoop's Core Theorem have been studied. The aim of this paper is to characterize a class of four-dimensional matrices, and so to obtain necessary and sufficient conditions for a new inequality related to the P- and sigma-cores.