@techreport {TR-1977-006,
   type = {Technical Report},
   author = {T.Beyer, S.Hedetniemi, S.Mitchell},
   title = {Shortest paths in trees},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1977-006,
   year = 1977,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1977-006.pdf}},
}