1. K. Huang andC. N. Yang:Phys. Rev.,105, 767 (1957);C. De Dominicis andP. C. Martin:Phys. Rev.,105, 1419 (1957);K. Huang:The Many Body Problem, edited byB. De Witt (London, 1958).
2. L. Gratton andG. Szamosi:Nuovo Cimento,30, 1056 (1965). We shall refer to this paper as GS in the sequel.
3. The important results that the upper limit to the velocity of sound isc notc/√3 was first obtained byZel’dovich (3). in his model based on a repulsive vector interaction among stationary point charges. Our model is another example that has this limit for the velocity of sound.
4. Ya. B. Zel’dovich:Sov. Phys. JETP,14, 1143 (1962).
5. The formula for pressure, eq. (15) of GS, was corrected subsequently in ref. (4).