Maria-Florina Balcan Alina Beygelzimer John Langford Agnostic active learning. 78-89 2009 75 J. Comput. Syst. Sci. 1 http://dx.doi.org/10.1016/j.jcss.2008.07.003 db/journals/jcss/jcss75.html#BalcanBL09