Miquel Ferrer Ernest Valveny Francesc Serratosa Median graph: A new exact algorithm using a distance based on the maximum common subgraph. 579-588 2009 30 Pattern Recognition Letters 5 http://dx.doi.org/10.1016/j.patrec.2008.12.014 db/journals/prl/prl30.html#FerrerVS09