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List:       python-list
Subject:    Re: Would there be support for a more general cmp/__cmp__
From:       Steve Holden <steve () holdenweb ! com>
Date:       2005-10-25 23:07:39
Message-ID: djmdrq$dq9$2 () sea ! gmane ! org
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Steven D'Aprano wrote:
> On Tue, 25 Oct 2005 10:09:29 -0400, Christopher Subich wrote:
> 
> 
>>>>By analogy, one can ask, "is the cat inside the box?" and get the answer
>>>>"No", but this does not imply that therefore the box must be inside the
>>>>cat.
>>>
>>>
>>>Bad analogy, this doesn't define a mathematical ordering, the subset
>>>relationship does.
>>
>>Yes, it does.  Consider "in" as a mathematical operator:
>>
>>For the set (box, cat-in-box)
>>
>>box in box: False
>>box in cat-in-box: False
>>cat-in-box in box: True
>>cat-in-box in cat-in-box: False
>>
>>For the set (box, smart-cat) # cat's too smart to get in the box
>>
>>box in box: False
>>box in smart-cat: False
>>smart-cat in box: False
>>smart-cat in smart-cat: False
>>
>>In both these cases, the "in" operator is irreflexive, asymmetric, and 
>>transitive (extend to mouse-in-cat if you really care about transitive), 
>>so "in" is a partial order sans equality.  A useless one, but a partial 
>>order nonetheless.
> 
> 
> What do you mean "in" is a useless ordering? It makes a huge difference
> whether "nuclear bomb in New York" is true or not.
> 
> In fact, I'm quite surprised that Antoon should object to "in" as "this
> doesn't define a mathematical ordering, the subset relationship does" when
> "subset" is just "in" for sets: set S is a subset of set T if for all
> elements x in S, x is also in T. Informally, subset S is in set T.
> 
> Can somebody remind me, what is the problem Antoon is trying to solve here?
> 
> 
Being Belgian, I suspect.

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
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