A Note on a Lemma of Zo

R. Fefferman
1986 Proceedings of the American Mathematical Society  
In this article we prove that a general class of singular integrals on product spaces maps L log L boundedly to weak L1. We use this to prove a theorem about maximal functions which generalize the strong maximal function. Introduction. In [1] Zo proved the following result:
doi:10.2307/2046161 fatcat:443waofzynfzxl6nw7qb6mf5zm