“…In [20] the authors used a subtle version of Calderón-Zygmund decomposition, which was pioneered by Fefferman [9] and later on developed by Christ [8], to study maximal functions. Fefferman's ideas turned out to be applicable to the discrete settings as it was shown in [20], and recently also in [12] and [7]. Heuristically speaking, the weak type (1, 1) bound of M h f is obtained by considering the recalcitrant part of the Calderón-Zygmund decomposition in ℓ 2 (see Lemma 6.6 and Theorem 6.1 in Section 6), using the fact that K h,N * f, K h,N * g = K h,N * K h,N * f, g , and decomposing K h,N * K h,N (x) 1 into several manageable pieces (a delta mass at 0, a slowly varying function G N (x), and a small error term E N (x), see Section 5) obtained by special Van der Corput estimates, (we refer to Section 3).…”