Xianmin Zheng PAD programming and its application in chemistry. 60-66 1989 29 Journal of Chemical Information and Computer Sciences 2 http://pubs.acs.org/cgi-bin/archive.cgi/jcisd8/1989/29/i02/f-pdf/f_ci00062a003.pdf db/journals/jcisd/jcisd29.html#Zheng89