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From: John Harris <niam@jghnorth.org.uk.invalid>
Newsgroups: comp.lang.javascript
Subject: Re: passing a set of numbers to a function
Date: Sat, 30 Jan 2016 10:10:06 +0000
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On Fri, 29 Jan 2016 16:11:31 +0000, Ben Bacarisse
<ben.usenet@bsb.me.uk> wrote:

>John Harris <niam@jghnorth.org.uk.invalid> writes:
>
>> On Fri, 29 Jan 2016 12:23:53 +0000, Ben Bacarisse
>> <ben.usenet@bsb.me.uk> wrote:
>>
>>>John Harris <niam@jghnorth.org.uk.invalid> writes:
>>>
>>>> On Fri, 29 Jan 2016 10:09:17 +0000, Ben Bacarisse
>>>> <ben.usenet@bsb.me.uk> wrote:
>>>>
>>>>   <snip>
>>>>>Sets don't contain duplicates
>>>>   <snip>
>>>>
>>>> How can you tell?
>>>
>>>x not in (S \ {x}).  |{x}| =3D 1.  x in S =3D> |S \ {x}| =3D |S| - 1. =
 These
>>>are inconsistent with my understanding of the metaphor of duplication
>>>(though I accept it might have other nuances for other people).
>>
>> It depends what you mean by |{x}| =3D 1. Possibly you mean
>>   a) x occurs only once in {x};
>> or possibly you mean
>>   b) x is a member of {x} but no other object is.
>
>I intended the conventional meaning of cardinality.
><snip>

With the conventional meaning, the cardinality being 1 means that
there is a bijection between {x} and the set {{}}. Being a bijection
relies on membership, not at all on multiplicity.

  John