Raphaël Clifford Klim Efremenko Benny Porat Ely Porat Amir Rothschild 99-108 2008 SPIRE http://dx.doi.org/10.1007/978-3-540-89097-3_11 conf/spire/2008 db/conf/spire/spire2008.html#CliffordEPPR08