Energetically best pseudoknots might be deeply buried under suboptimal solutions. To make them visible we could apply a binary classification algebra. One class for nested structures, the other class for pseudoknots. Here, we want to differentiate between four classes, namly

The algebra requires an answer type with four states. We use two booleans: isH and isK. The only affected rules are cadd, pknot and pkiss.

An application of enforced pseudoknot computation is e.g. KnotInFrame.