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Astron. Astrophys. 359, 1-8 (2000) AcknowledgementsI would like to thank Gaetano Scarpetta and Salvatore Capozziello for their helpful comments on the manuscript. Work supported by fund ex 60% D.P.R. 382/80. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 2000 Online publication: June 30, 2000 ![]() |