Chengming Qi Yingjie Tian Shoumei Cui Yunchuan Sun Concept Semilattice: Construction and Complexity. 1849-1853 2008 ICYCS http://dx.doi.org/10.1109/ICYCS.2008.157 conf/icycs/2008 db/conf/icycs/icycs2008.html#QiTCS08