Shile Gao Kequan Ding A graphical criterion of planarity for RNA secondary structures with pseudoknots in Rivas-Eddy class. 47-56 2008 395 Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.tcs.2007.09.026 db/journals/tcs/tcs395.html#GaoD08