Lopamudra Mukherjee Vikas Singh Jiming Peng Jinhui Xu Michael J. Zeitz Ronald Berezney Generalized median graphs and applications. 21-44 2009 17 J. Comb. Optim. 1 http://dx.doi.org/10.1007/s10878-008-9184-7 db/journals/jco/jco17.html#MukherjeeSPXZB09