“…When u = 1, T f (•, 1) is a classical operator in harmonic analysis. For some related results, we refer to [21,28,29,40,41] and the references therein. In this section, our main goal is to determine the almost optimal range of exponents ( 1p , 1 q ) such that the L p x (R 2 ) → L q x (R 2 ) estimate for T holds uniformly for u ∈ [1,2].…”