Are QSOs gravitationally lensed

There are now four known cases of multiply imaged QSOs. In this paper, the author argues that although the exciting search for multiply imaged QSOs has only begun, sufficient data already exist to test two hypotheses: (A) QSOs are intrinsically luminous and occasionally are multiply imaged through a chance alignment with a foreground galaxy of sufficient mass gradient and (B) all QSOs are the result of gravitational lens magnification of a distant Seyfert nucleus by foreground galaxy(s). The former is found to predict numbers in good agreement with current catalogues, using canonical values for velocity dispersion and fraction of mass in galaxies as well as for average amplification in lens events that give secondary images. (Auth.)