A ribonucleic acid (RNA) molecule is the helical configuration of a primary structure of nucleotides, A, G, U and C, together with Watson-Crick (A-U, G-C) and (U-G) base pairs. It is well-known that RNA structures exhibit cross-serial nucleotide interactions, called pseudoknots. First recognized in the turnip yellow mosaic virus in , they are now known to be widely conserved in functional RNA molecules. Modular k-noncrossing diagrams represent a model of RNA pseudoknot structures that is RNA structures exhibiting cross-serial base pairings. The particular case of modular noncrossing diagrams, i.e. RNA secondary structures has been extensively studie...