Recovering Singular Integrals from Haar Shifts

Abstract

Any sufficiently smooth one-dimensional Calderon-Zygmund convolution operator is the average of Haar shift operators. The latter are dyadic operators which can be efficiently expressed in terms of the Haar basis. This extends the result of S. Petermichl on restoring Hilbert transform via Haar shift operators, a technique that has become fundamental to the analysis of these operators.