Sjur Refsdal. On the possibility of determining Hubble's parameter and the masses of galaxies from the gravitational lens effect. MNRAS. 1964, 128 (4): 307–310. Bibcode:1964MNRAS.128..307R. doi:10.1093/mnras/128.4.307.
Sjur Refsdal. On the possibility of determining Hubble's parameter and the masses of galaxies from the gravitational lens effect. MNRAS. 1964, 128 (4): 307–310. Bibcode:1964MNRAS.128..307R. doi:10.1093/mnras/128.4.307.