Cristina Coppola Giangiacomo Gerla Tiziana Pacelli Convergence and fixed points by fuzzy orders. 1178-1190 2008 159 Fuzzy Sets and Systems 10 http://dx.doi.org/10.1016/j.fss.2007.12.006 db/journals/fss/fss159.html#CoppolaGP08