Richie Chih-Nan Chuang Ashim Garg Xin He Ming-Yang Kao Hsueh-I Lu Compact Encodings of Planar Graphs via Canonical Orderings and Multiple Parentheses http://arxiv.org/abs/cs.DS/0102005 2001 CoRR cs.DS/0102005 db/journals/corr/corr0102.html#cs-DS-0102005 informal publication