Re: higher-order logic

From: H. Enderton (hbe_at_sonia.math.ucla.edu)
Date: 01/30/05

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    Date: Sun, 30 Jan 2005 22:42:13 +0000 (UTC)
    
    

    alex goldman <hello@spamm.er> wrote:
    >By the way, is the term "higher-order logic" ever used in a sense different
    >from "second-order logic"? Since second-order logic allows quantification
    >over relations, would third-, etc. order logics allow quantification over
    >quantifiers or something similarly outlandish?

    It's simpler than that.
    First order: quantify over individuals
    Second order: quantify over sets of individuals and relations on individuals.
    Third order: quantify over sets of sets of individuals (and relations on
    relations on individuals).

    Quibble: Church actually used a slightly more refined way of counting
    third, fourth, ... order.

    > I'm interested in learning more about higher-order logic
    > (...)
    >I was hoping to find a non-advocacy review of main results in higher-order
    >logic (as opposed to first-order logic).

    You said (in the original post) no plugs, so I won't say anything
    about Chapter 4 of my logic book.

    --Herb Enderton


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