S. K. Mishra Shouyang Wang Kin Keung Lai Symmetric duality for minimax mixed integer programming problems with pseudo-invexity. 37-42 2009 198 European Journal of Operational Research 1 http://dx.doi.org/10.1016/j.ejor.2008.08.016 db/journals/eor/eor198.html#MishraWL09