@TechReport{odersky:critical-pairs,
  author = 	"Martin Odersky",
  title = 	"A Syntactic Method for Proving Observational
                 Equivalences",
  institution =	{Department of Compter Science, Yale University},
  type =	{Research Report},
  number =	{YALEU/DCS/RR-964},
  year = 	1993,
  month = 	"May"
}