 
Summary: 1
A REMARK ON MAXIMAL OPERATORS ALONG DIRECTIONS IN
R2
ANGELES ALFONSECA, FERNANDO SORIA, AND ANA VARGAS
Abstract. In this paper we give a simple proof of a longstanding conjecture, recently
proved by N. Katz, on the weaktype norm of a maximal operator associated with an
arbitrary collection of directions in the plane. The proof relies upon a geometric
argument and on induction with respect to the number of directions. Applications
are given to estimate the behavior of several types of maximal operators.
1. Introduction
Let be a subset of [0,
4 ). Associated to it, we define the maximal operator M
acting on locally integrable functions f on R2 by
Mf(x) = sup
xRB
1
R R
f(y) dy,
where B denotes the basis of all rectangles with longest side forming an angle with
the xaxis, for some .
