  I give a mini-survey of several approaches to the $A_2$ 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 $A_p$--$A_\infty$ testing conditions, and
the two-weight $T1$ theorem for positive dyadic operators).
