Fig. 3
From: Automated design of dynamic programming schemes for RNA folding with pseudoknots
a minimal expansion of a fatgraph, with every helix of length 5, and no unpaired base. The associated graph consists of one vertex per base, and one edge per base pair and backbone link. b A helix of length l in an RNA graph, as per the latter definition. c Given a helix in a graph G, the treewidth of G is either equal to \(tw(G_\boxtimes )\) or \(tw(G_\boxslash )\). Each case is associated with a type of separator that can be used to extend the helix, or insert bulges, without changing the treewidth. (d) The dotted line represents a “hop-edge” which, if represented in a given tree decomposition of G, can be used to obtain \(G_\boxtimes\) as a minor of G, showing that the helix is in the “clique” case