“…Submodularity of functions over finite sets plays an important role in discrete optimization (see, e.g., [12], [13], [5], [18], [16], [2], [19], [20], [6], [7], [15], [21], [1], [9], and [10]). It has been shown that, under submodularity, the greedy strategy provides at least a constant-factor approximation to the optimal strategy.…”