Amnon Ta-Shma Christopher Umans David Zuckerman Lossless Condensers, Unbalanced Expanders, And Extractors. 213-240 2007 27 Combinatorica 2 http://dx.doi.org/10.1007/s00493-007-0053-2 db/journals/combinatorica/combinatorica27.html#Ta-ShmaUZ07