@TECHREPORT{R18,
  key    =       {R18},
  AUTHOR =	 {Christoph Benzm{\"u}ller and Chad E. Brown and Michael Kohlhase},
  TITLE =	 {Higher Order Semantics and Extensionality.},
  INSTITUTION =	 {Carnegie Mellon University, Pittsburgh, PA},
  YEAR =	 2003,
  pages =        {1--74},
  TYPE =	 {Technical Report},
  NUMBER =	 {CMU-01-03},
  ABSTRACT =	 {In this paper we re-examine the semantics of classical higher order
                  logic with the purpose of clarifying the role of extensionality. To
                  reach this goal, we distinguish nine classes of higher order models with
                  respect to various combinations of Boolean extensionality and three
                  forms of functional extensionality. Furthermore, we develop a
                  methodology of abstract consistency methods (by providing the necessary
                  model existence theorems) needed to analyze completeness of
                  (machine-oriented) higher order calculi with respect to these model
                  classes.},
  chrisnote =	 {R22},
  url =		 {www.ags.uni-sb.de/~chris/papers/R22.pdf}
}