Carlos Ansótegui Ramón Béjar Cèsar Fernández Carles Mateu Edge Matching Puzzles as Hard SAT/CSP Benchmarks. 560-565 2008 CP http://dx.doi.org/10.1007/978-3-540-85958-1_42 conf/cp/2008 db/conf/cp/cp2008.html#AnsoteguiBFM08a