Christopher Jefferson Serdar Kadioglu Karen E. Petrie Meinolf Sellmann Stanislav Zivný Same-Relation Constraints. 470-485 2009 CP http://dx.doi.org/10.1007/978-3-642-04244-7_38 conf/cp/2009 db/conf/cp/cp2009.html#JeffersonKPSZ09