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2. J. Blietschau et al., Nucl. Phys. B114(1976) 189.
3. For a recent review see, for example, F. Niebergall in Proceedings of the International Conference Neutrino ’82, Balatonfured, Hungary 1982 (Budapest, 1982 ) Volume II, p. 62.
4. C.Y. Prescott et al., Phys. Letters 77B(1978) 347 and 84B(1979) 524.
5. Report by B. Borgia (CHARM Collaboration), these proceedings.