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2. A.D.B. Woods, Phys. Rev. 136, A 781 (1964).
3. J.C. Williams, D. de Fontaine, and N.E. Paton, Metall. Trans. 4, 2701 (1973); S.C. Moss, D.T. Keatings, and J.D. Axe, Solid State Commun. 13, 1465 (1973).
4. N. Wakabayashi and J.G. Traylor, to be published.
5. H.G. Smith, in Superconductivity in d- and f-band metals, ed. by D.H. Douglass (AIP, New York, 1972); H.G. Smith and W. Glesser, in Proceedings of the International Conference on Phonons, Rennes, France, 1971, ed. by M.A. Musimovici ( Flammarion, Paris, 1972 ) p. 145.