Usability: Formalising (un)definedness in typed lambda calculi

Jan Kuper, L. Pacholski (Editor), J. Tiuryn (Editor)

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    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.
    Original languageUndefined
    Number of pages15
    Publication statusPublished - 1995


    • EWI-11087
    • IR-61923

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