Çakan, CelalAltay, BilalCoşkun, Hüsamettin2020-11-052020-11-052009ÇAKAN C,ALTAY B,ÇOŞKUN H (2009). $\sigma$-regular matrices and A $\sigma$- core theorem for double sequences. Hacettepe Journal of Mathematics and Statistics, 38(1), 51 - 58.https://app.trdizin.gov.tr/makale/T1RJME5EazUhttps://hdl.handle.net/11616/18631Abstract: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 σ-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 σ-cores.eninfo:eu-repo/semantics/openAccessArticle