When two become one: an apparent QSO pair turns out to be a single quasar G. Cupani, S. Cristiani, V. D’Odorico, B. Milvang-Jensen and J.-K. Krogager A&A, 529 (2011) A99 Published online: 11 April 2011 DOI: 10.1051/0004-6361/201116786