MATHEMATICA SLOVACA, cilt.60, sa.4, ss.495-506, 2010 (SCI-Expanded)
A lower triangular infinite matrix is called a triangle if there are no zeros on the principal diagonal. The main result of this paper gives a minimal set of sufficient conditions for a double triangle T to be a bounded operator on A(k)(2); i.e., T is an element of B (A(k)(2)) for the sequence space A(k)(2) defined below. As special summability methods T we consider weighted mean and double Cesaro, (C, 1, 1), methods. As a corollary we obtain necessary and sufficient conditions for a double triangle T to be a bounded operator on the space BV of double sequences of bounded variation.