Examples of structures not designed by RNA-SSD. Structures not designed by RNA-SSD have short stems separated by loops, indicated by arrows in the Figure. (a) Random structure of length 450 (RND-450-n84). This is the only random structure in our data set that RNA-SSD did not design. Note that it has two internal loops separated only by one base pair. (b) Biologically motivated structure of length 74 (BIOM-50-n262).