Everyone, my response time will slow as I travel by car from Maine to Texas.
Raul, I will think about your suggestion which is attractively simple.
One thing I have noticed is that when you deal with the power set of a power
set, it helps to have a "visible" empty set, i.e. compare
]E =: , < i.0 0 NB. empty set
++
++
]phi =: '' NB. empty
On the other hand, having even an unobtrusive set marker at the end of every
set
may be too "clunky". On the OTHER hand, it helps to have only one kind of set,
boxed, versus one open and the others boxed. As Lil' Abner used to say, Sigh...
Fraser Jackson showed me a neat way to construct power sets. I hope he will
show you soon. As this is the programming forum, you can try to come up with
your own neat way.
The power set of a set is the new set comprising all subsets of the original
set. It gets its name from the fact that the power set has 2^k elements if the
original set has k elements. The power set of the set {0,1} has the elements
{}, {0}, {1}, and {0,1) -- four elements.
... signing off now until the next stop.
Kip
Raul Miller wrote:
> On Fri, Jul 31, 2009 at 8:13 AM, Kip Murray<[email protected]> wrote:
>> 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.
>
> I do not understand why you do not use empty sequence
> to represent empty set.
>
> isset=: (-: /:~) *. (-: ~.@,) *. -:&'' +. 0 < L.
>
> seems simple enough.
>
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