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Flat cosmological models with a cosmological term varying as Lambda = (alpha)(R exp -2) + (beta)(H squared) + gamma are investigated. Exact expressions for observable quantities are obtained and some of their properties discussed. The lookback time-redshift, the luminosity distance-redshift, the angular diameter distance-redshift, and the comoving volume derivative-redshift diagrams for some selected world models are also presented.
I. Waga (Wed,) studied this question.