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2. L.I. Ponomarev, Contemporary Physics 31, 219 (1991).
3. H.K. Walter, this conference, S.Monti, ENEA NUC-RIN Bologna, int. report (1991).
4. L.I. Men’shikov, Muon Catal. Fusion 2, 173 (1988).
5. see W. Chaplinski et al., Muon Catal. Fusion 5, 59 (1990), and references given therein.