@techreport {TR-1980-005,
   type = {Technical Report},
   author = {Andrzej Proskurowski },
   title = {K-trees: representations and distances},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1980-005,
   year = 1980,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1980-005.pdf}},
}