On Membranes and Plates.

1 Weyl, H., "Almost Periodic Invariant Vector Sets in a Metric Vector Space," Am. J. Math., 71, 178-205 (1949). 2 Neumann, J. v., "Almost Periodic Functions in a Group I," Trans. A.M.S., 36, 445492 (1934). 3 Bochner, S., and Neumann, J. v., "Almost Periodic Functions in a Group II," Ibid., 37, 21-50 (1935). 4 Maak, W., "Moduln fastperiodischer Funktionen," Abh. Math. Sem. Hamburg Univ. 16, 56-71 (1949). .Maak, W., "Abstrakte fastperiodische Funktionen," Ibid., 11, 367-380 (1936).