Marco Tomassini Leonardo Vanneschi Negative Slope Coefficient and the Difficulty of Random 3-SAT Instances. 643-648 2008 EvoWorkshops http://dx.doi.org/10.1007/978-3-540-78761-7_70 conf/evoW/2008 db/conf/evoW/evoW2008.html#TomassiniV08