Jun Liu Yuansheng Jiang New Method for Constructing Isospectral Graphs. 1267-1272 1994 34 Journal of Chemical Information and Computer Sciences 6 http://pubs.acs.org/cgi-bin/archive.cgi/jcisd8/1994/34/i06/f-pdf/f_ci00022a007.pdf db/journals/jcisd/jcisd34.html#LiuJ94