Usability: formalising (un)definedness in typed lambda calculus

  • Jan Kuper
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 933)


In this paper we discuss usability, and propose to take that notion as a formalisation of (un)definedness in typed lambda calculus, especially in calculi based on PCF. We discuss some important properties that make usability attractive as a formalisation of (un)definedness. There is a remarkable difference between usability and solvability: in the untyped lambda calculus the solvable terms are precisely the terms with a head normal form, whereas in typed lambda calculus the usable terms are “between” the terms with a normal form and the terms with a (weak) head normal form.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • Jan Kuper
    • 1
  1. 1.Department of Computer ScienceUniversity of TwenteAE EnschedeThe Netherlands

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