As it happens, set box is the empty set. It is a good thing that _nothing_ is
an element of set box . Not allowing i.0 0 to be an element is the price I pay
for having an empty set in this model of finite set theory.
set box
++
++
E is set box
1
}: set box NB. curtail
In this model, elements are in boxes of the curtail of a set.
Raul Miller wrote:
> On Fri, Jul 31, 2009 at 7:33 AM, Kip Murray<[email protected]> wrote:
>> Yes, the argument to verb set must be a box or list of boxes, and (i.0 0) -:
>> empty '' is neither.
>
> Ok, sorry, I expressed my example incorrectly.
>
>> For what it's worth, every array except i.0 0 (used in the "set marker" box)
>> is
>> allowed to be an element of a set.
>
> Yes, that was the issue which I was questioning:
>
> box=: <i.0 0
> box iselement set box
> 0
>
> I do not see the value of this restriction.
>
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