Figure 2.

SSR equivalence classes for a fixed partition of the inputs

$S_0$ is always assigned ε, so it is represented by a gray node. A blue link between $S_i$ and an $S_j$ denotes that $\text{ISCOMP}\left(t\left(i\right)\text{,}t\left(j\right)\right)=\text{true}$. The equivalence classes are determined by the Watson-Crick complementary relationships between the rest of the parts, i.e. by all the possible ways to draw the blue links.