“…Similar results for the two-dimensional case can be found in Nagy [23,24], Nagy and Tephnadze [25,26,27,28]. Approximation properties of general summability methods can be found in [2,5,7,8,2,21] (see also [17,18]). Fridli, Manchanda and Siddiqi [12] improved and extended results of Móricz and Siddiqi [22] to Martingale Hardy spaces.…”