2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8982We collected from literature the information about large-separated pairs of QSOs, which however once were suspected as gravitationally lensed system. We discuss some new results on time delay determinations including optical-radio correlations for QSO 0957+561. We considered some possible observational effects of gravitational lensing by a cosmic string. A future international project for observations of the gravitational lens system UM425 is briefly discussed.9 pagesAstrophysicstext