@TechReport{birkedal+:rel-interp-tr,
  author = 	 {Lars Birkedal and Robert Harper},
  title = 	 {Relational Interpretation of Recursive Types in an Operational Setting},
  institution =  {Carnegie Mellon University Computer Science Department},
  year = 	 1998,
  number =	 {CMU-CS-98-125},
  address =	 {Pittsburgh, PA},
  month =	 {April}
}