Figure 3(b): To find R_br, find bs that precede rs. I show two copies of F for clarity. Working right-to-left, the copy on the right represents the previous range, and the one on the left is new. To search: 1. Take all blocks starting with b; 2. search this set for the first i where FL[i]startp, and the last j where FL[j]<=endp; everything in this [i,j] range must map into the target interval between startp and endp. This [i,j] interval identifies all bs that are followed by r; in other words, all blocks starting with "br." i and j become the new startp/endp for the next step.
