From: <jvoosten@math.uu.nl>
To: categories@mta.ca
Subject: Re: Realizability and Partial Combinatory Algebras
Date: Tue, 18 Feb 2003 12:48:48 +0100 (CET) [thread overview]
Message-ID: <200302181148.MAA14451@kodder.math.uu.nl> (raw)
Dear John,
> Note that we can find elements if,true,false \in A satisfying
> if true x y = x, if false x y = y,
> and furthermore we can arrange that true = k.
> (I'll use "if then else" syntax below).
> We want to construct S such that (in A),
> Skxkykz ~ (xkz)k(ykz), and Skxky is always defined.
> Take S to be
> \lambda txuyvz. if v then (xkz)k(ykz) else false
> using the usual Curry translation of lambda terms. To see that
> Skxky is always defined, note that, provably, Skxky(false)z = false.
There is a point I don't understand. If I work out Skxky, then I find
a term which contains subterms of the form xk, yk. So how can this be
defined if x or y represent nowhere defined functions?
It looks to me, that you are using a form of Combinatorial Completeness
that is not valid with the weaker S-axiom. If I am correct, one has
the following form of Combinatorial Completeness:
For every term t and variable z, there is a term \lambda z.t with the
property:
If \lambda z.t is defined, then for each a, (\lambda z.t)a ~ t[a/z]
(of course, a really correct version has more than one variable)
Best, Jaap
next reply other threads:[~2003-02-18 11:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-02-18 11:48 jvoosten [this message]
2003-02-18 18:34 ` Peter Lietz
-- strict thread matches above, loose matches on Subject: below --
2003-02-20 16:44 jvoosten
2003-02-21 15:03 ` Peter Lietz
2003-02-07 23:43 Realizibility " Prof. Peter Johnstone
2003-02-12 10:58 ` Realizability " John Longley
2003-02-13 17:34 ` Peter Lietz
2003-02-17 15:27 ` John Longley
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