Phillip Helbig
"The image separation-source redshift relation for gravitational lenses as a cosmological test"
MNRAS, 298, 2, 395–398 (1 August 1998)
free, full, official version | doi:10.1046/j.1365-8711.1998.01692.x | ADS: 1998MNRAS.298..395H | Google Scholar