] References ^ Bock, R. K.; et al ( 2008 - 06-27 ). "Very-High-Energy Gamma Rays from a Distant Quasar: How Transparent Is the Universe?". Science 320 (5884): pp 1752–1754. doi : 10.1126/science.1157087 . ISSN 0036-8075 . ^ Rothkamm K. - Evidence for a lack of DNA double-strand break repair in