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Published online by Cambridge University Press: 19 March 2013
We prove results about the Lp-almost-periodicity of convolutions. One of these follows from a simple but rather general lemma about approximating a sum of functions in Lp, and gives a very short proof of a theorem of Green that if A and B are subsets of {1,. . .,N} of sizes αN and βN then A+B contains an arithmetic progression of length at least
\begin{equation}\exp ( c (\alpha \beta \log N)^{1/2} - \log\log N).\end{equation}
\begin{equation}\exp\biggl( c \biggl(\frac{\alpha \log N}{\log^3 2\beta^{-1}} \biggr)^{1/2} - \log( \beta^{-1} \log N) \biggr).\end{equation}