References for the idea of backtracking 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://www.st.ewi.tudelft.nl/sat/theses/jantien.pdf ) - Section 5.2 - page 27.