@techreport {TR-1991-007,
   type = {Technical Report},
   author = {Jan Telle, Andrzej Proskurowski},
   title = {Efficient Sets in Partial k-trees},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1991-007,
   month = 3,
   year = 1991,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1991-007.pdf}},
}