1. M.L.G.Foy, N.Heimann, W.J.Kossler, and C.E.Stronach, Phys. Rev. Lett. 30, (1973) 1064.
2. The measurements at Dubna have been summarized in [3], and the work of the Tokyo group is reviewed in [4]. For a summary at the first ?SR-conference at Rorschach, see [5]. The most comprehensive survey is the recent review by the Zurich group [6]. For a pedagogical introduction, see [7].
3. I.I.Gurevich, A.I.Klimov, V.N.Maiorov, E.A.Meleshko, B.A.Nikol'skii, V.I.Selivanov, and V.A.Suetin, Zh. Eksp. Teor. Fiz. 69 (1975) 439, [Sov. Phys. JETP 42 (1976) 222].
4. N.Nishida, K.Nagamine, R.Hayano, T.Yamazaki, D.Fleming, R.A.Duncan, J.H.Brewer, A.Ahktar, and H.Yasuoka, J. Phys. Soc. Jpn. (1978) 1131.
5. A.T.Fiory, Hyperfine Interact. 6 (1979), 63