@techreport {TR-1980-024,
   type = {Technical Report},
   author = {Sandra Hedetniemi, Stephen Hedetniemi, Peter Slater},
   title = {Centers and Medians of C(N) -Trees*},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1980-024,
   year = 1980,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1980-024.pdf}},
}