Zengfu Wang Bill Moran 0001 Xuezhi Wang 0001 Quan Pan 0001 Approximation for maximizing monotone non-decreasing set functions with a greedy method. 29-43 2016 31 J. Comb. Optim. 1 https://doi.org/10.1007/s10878-014-9707-3 db/journals/jco/jco31.html#WangMWP16