A remark on a paper of P. B. Djakov and M. S. Ramanujan

Uyanik E., YURDAKUL M. H.

TURKISH JOURNAL OF MATHEMATICS, cilt.43, ss.2494-2498, 2019 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 43 Konu: 5
  • Basım Tarihi: 2019
  • Doi Numarası: 10.3906/mat-1905-90
  • Sayfa Sayıları: ss.2494-2498


Let l be a Banach sequence space with a monotone norm in which the canonical system (e(n)) is an unconditional basis. We show that if there exists a continuous linear unbounded operator between l-Kothe spaces, then there exists a continuous unbounded quasidiagonal operator between them. Using this result, we study the corresponding Kothe matrices when every continuous linear operator between l-Kothe spaces is bounded. As an application, we observe that the existence of an unbounded operator between l-Kothe spaces, under a splitting condition, causes the existence of a common basic subspace.