We give a self-contained exposition of the recent remarkable result of Kelley and Meka: if
has no nontrivial three-term arithmetic progressions then
,
where
is a constant.
Although our proof is identical to that of Kelley and Meka in all of the main
ideas, we also incorporate some minor simplifications relating to Bohr sets.
This eases some of the technical difficulties tackled by Kelley and Meka
and widens the scope of their method. As a consequence, we improve the
lower bounds for the problem of finding long arithmetic progressions in
, where
.