An upper limit to the variation in the fundamental constants at redshift z = 5.2 S. A. Levshakov, F. Combes, F. Boone, I. I. Agafonova, D. Reimers and M. G. Kozlov A&A, 540 (2012) L9 Published online: 02 April 2012 DOI: 10.1051/0004-6361/201219042