Fig. 1From: Automatic generation of pseudoknotted RNAs taxonomyOn the top, an RNA secondary structure illustrated via an arc-diagram. The motif in part a is pseudoknot-free, while the one in part b is pseudoknotted. Pseudoknots are clearly visible as crossings of arcs. On the bottom, the three feasible relations: c concatenation, d nesting and e crossing of two bondsBack to article page