Adam Kasperski Pawel Zielinski Using Gradual Numbers for Solving Fuzzy-Valued Combinatorial Optimization Problems. 656-665 2007 conf/ifsa/2007 IFSA (1) http://dx.doi.org/10.1007/978-3-540-72950-1_65 db/conf/ifsa/ifsa2007.html#KasperskiZ07