Figure 10
Distance of two structures. Positions paired differently in S1 and S2 are assigned a "1". There are two types of positions: I. p is contained in different arcs, see position 4, (4, 20) ∈ S1 and (4, 17) ∈ S2. II. p is unpaired in one structure and p is paired in the other, such as position 18.