Benjamin W. Wah Zhe Wu Penalty Formulations and Trap-Avoidance Strategies for Solving Hard Satisfiability Problems. 3-17 2005 20 J. Comput. Sci. Technol. 1 http://www.springerlink.com/index/10.1007/s11390-005-0002-8 db/journals/jcst/jcst20.html#WahW05