NOTES ON SCONING AND RELATORS John Mitchell and Andre Scedrov ABSTRACT. A semantics of typed lambda calculi based on relations is described. The main mathematical tool is a category-theoretic method of sconing, also called glueing or Freyd covers. Its correspondence to logical relations is also examined. In the case of polymorphic types, a central role is played by relators, i.e., maps that take objects to objects and relations to relations. Sconing may be used to express relators as functors, indeed, as certain object maps on an appropriate category. These notes are intended to be accessible to readers with minimal background in category theory. Available using anonymous ftp from host ftp.cis.upenn.edu and the file pub/papers/scedrov/rel.dvi or pub/papers/scedrov/rel.ps . ==============================================================================