The A2 theorem: Remarks and complements
Abstract
I give a mini-survey of several approaches to the A2 theorem, biased towards the "corona" rather than the "Bellman" side of the coin. There are two new results (a streamlined form of Lerner's local oscillation formula, and the sharpness of the linear-in-complexity weak (1,1) bound for dyadic shifts) and two new proofs of known results (the Ap--A∞ testing conditions, and the two-weight T1 theorem for positive dyadic operators).
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