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3. D. P. Stanley andD. Robson:Phys. Rev. D,21, 3180 (1980)
4. S. Ishida:Prog. Theor. Phys.,46, 1570, 1905 (1971)
5. S. Ono andF. Schöberl:Phys. Lett. B,118, 419 (1982).