title: Finding the minimal coverage of an interval with subintervals
body: <p>Suppose I have an interval (a,b), and a number of subintervals {(a<sub>i</sub>,b<sub>i</sub>)}<sub>i</sub> whose union is all of (a,b).  Is there an efficient way to choose a minimal-cardinality subset of these subintervals which still covers (a,b)?</p>