[FOM] An intuitionistic query
rgheck
rgheck at brown.edu
Fri Sep 11 11:10:31 EDT 2009
On 09/09/2009 10:12 AM, Arnold Neumaier wrote:
> For any of these interpretations, I have a related question.
> Is the following intuitive implication
> A={a,b,c} ==> |A|=1 v |A|=2 v |A|=3 (**)
> intuitionistically valid?
>
>
No. For a simpler case, let A = {a,b}, where we do not have a = b v a <>
b. This last will clearly follow from |A| = 1 v |A| = 2.
> (*) is a special case of Dirichlet's pigeonhole principle.
> Are there versions of the latter that are intuitionistically
> undecidable? I found an infinite version in
> https://eprints.kfupm.edu.sa/60600/1/60600.pdf ,
> but I am looking for a finite version.
>
>
Each of the finite versions is certainly going to be provable by a
version of the argument you gave, and the uniformity of those arguments
is good intuitionistic reason to think the generalization holds. I.e,
the obvious argument by induction should work.
Richard
--
-----------------------
Richard G Heck Jr
Professor of Philosophy
Brown University
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