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Abstract

This communication describes the lessons we have to draw after the observation of neutrinoless ββ decay on a 6σ level by the enriched ⁷⁶Ge experiment in Gran Sasso, for present and future experiments (a) to fulfill the task to confirm the present result (b) to deliver additional information on the main contributions of effective neutrino mass and right-handed weak currents etc. to the 0νββ amplitude. It is pointed out that presently running and planned experiments are not sensitive enough to check the present evidence on a reasonable time scale. More important, the only way to get information on the individual contributions of m, η, λ etc to the 0νββ amplitude is to go to completely different types of experiments, e.g. mixed-mode β⁺EC decay experiments, such as ¹²⁴Xe decay, on a 10²⁷ y sensitivity level.