Bhaskar DasGupta Xin He Tao Jiang Ming Li John Tromp On the Linear-Cost Subtree-Transfer Distance between Phylogenetic Trees. 176-195 1999 25 Algorithmica 2-3 http://link.springer.de/link/service/journals/00453/bibs/25n2p176.html db/journals/algorithmica/algorithmica25.html#DasGuptaHJLT99