Chang, K.; Refsdal, S. (6 de diciembre de 1979). «Flux variations of QSO 0957+561 A, B and image splitting by stars near the light path». Nature282: 561-564. Bibcode:1979Natur.282..561C. doi:10.1038/282561a0.
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Chang, K.; Refsdal, S. (6 de diciembre de 1979). «Flux variations of QSO 0957+561 A, B and image splitting by stars near the light path». Nature282: 561-564. Bibcode:1979Natur.282..561C. doi:10.1038/282561a0.