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B.J. Boyle, Roberto J. Terlevich. The cosmological evolution of the QSO luminosity density and of the star formation rate. „Monthly Notices of the Royal Astronomical Society”. 293 (2), s. L49-L51, styczeń 1998. DOI: 10.1046/j.1365-8711.1998.01264.x. Bibcode: 1998MNRAS.293L..49B. (ang.).