@techreport {TR-1991-006,
   type = {Technical Report},
   author = {Renganathan Sundararajan},
   title = {An Abstract Interpretation Scheme for Groundness, Freeness, and Sharing  Analysis of Logic Programs},
   institution = {University of Oregon, Computer and Information Sciences Department},
   number = TR-1991-006,
   month = 10,
   year = 1991,
   note = {Available at \url{https://www.cs.uoregon.edu/Reports/TR-1991-006.pdf}},
}