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arXiv · 1501.05818

An elementary proof of the $A_2$ Bound

Michael T. Lacey
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Abstract

A martingale transform $ T$, applied to an integrable locally supported function $ f$, is pointwise dominated by a positive sparse operator applied to $ \lvert f\rvert $, the choice of sparse operator being a function of $ T$ and $ f$. As a corollary, one derives the sharp $ A_p$ bounds for martingale transforms, recently proved by Thiele-Treil-Volberg, as well as a number of new sharp weighted inequalities for martingale transforms. The (very easy) method of proof (a) only depends upon the weak-$L^1$ norm of maximal truncations of martingale transforms, (b) applies in the vector valued setting, and (c) has an extension to the continuous case, giving a new elementary proof of the $ A_2$ bounds in that setting.

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Michael T. Lacey. 2015-10-12. An elementary proof of the $A_2$ Bound. https://doi.org/10.1007/s11856-017-1442-x

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