Double Sequence Spaces and Four-Dimensional Matrices

Dr. Feyzi Basar is a Professor Emeritus since July 2016 at Inönü University, Turkey. He has published three books for graduate students and researchers and more than 160 scientific papers in the field of summability theory, sequence spaces, FK-spaces, Schauder bases, dual spaces, matrix transformations, spectrum of certain linear operators represented by a triangle matrix over some sequence spaces, the alpha-, beta- and gamma-duals and some topological properties of the domains of some double and four-dimensional triangles in certain spaces of single and double sequences and sets of the sequences of fuzzy numbers. Nowadays, Professor Basar works on the development of sequences and series, and the basic concepts of summability in non-newtonian calculus. He has guided 17 MA and 10 Ph.D. students and served as a referee for 141 international scientific journals. He is reviewer Mathematical Reviews since 2007 and Zentralblatt MATH, and the member of editorial boards of 21 scientific journals. He is also a member of scientific committees of 17 mathematics conferences, delivered talks at 14 different universities as an invited speaker, and worked on 10 scientific project, and participated in more than 70 mathematics symposiums with papers.Dr. Medine Yesilkayagil Savasci is an Associated Professor at Usak University. She has published more than 25 scientific papers in the field of summability theory, sequence spaces, FK-spaces, Schauder bases, dual spaces, matrix transformations, spectrum of certain linear operators represented by a triangle matrix over some sequence spaces, the alpha-, beta- and gamma-duals and some topological properties of the domains of some double and four-dimensional triangles in certain spaces of single and double sequences. She is reviewer Mathematical Reviews since 2017 and reviews in 11 international