References for the idea of recursive swapping algorithm:

• Michael Marte - Models And Algorithms For School Timetabling - A Constraint Programming Approach - 5 July 2002 ( free, on the internet, one possible link is: http://www.pms.ifi.lmu.de/publikationen/dissertationen/PMS-DISS-2003-1/PMS-DISS-2003-1.pdf ) - Section 2.2.5 - Manual Timetabling - pages 23-24.
• Jantien Hartog - Timetabling on Dutch High-Schools - Satisfiability versus gp-Untis - March 2007 ( free, on the internet, one possible link is: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.116.4715&rep=rep1&type=pdf ) - Section 5.2 - page 27.