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Pionium or A2pi is a hydrogen-like atom consisting of pi+ and pi- mesons. The lifetime of this atom is inversely proportional to the squared difference between the S-wave pipi scattering lengths for isospin 0 and 2, |a0 - a2|. This value is predicted by chiral perturbation theory (ChPT), and a measurement of the pi+pi- atom lifetime provides a possibility to check predictions of ChPT in a model-independent way.