INTRODUCTION Sixty years ago Sidon [7] asked, in the course of some investigations of Fourier series, for a sequence a1 < a2... for which the sums ai + aj are all distinct and for which ak tends to infinity as slowly as possible. Sidon called these sequences, B2 sequences. The greedly algorithm gives ak ¿ k and this was the best result until Atjai, Komlos and Szemeredi [1] found a B2 sequence s...