Re: Single element of set



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Alan Cameron Wills (alan@trireme.com)
Mon, 01 May 2000 17:38:18 +0100


sj_cook@uk.ibm.com wrote: > One thing I don't understand. > > If FlatSets have all the axioms of Set, then it must be possible to prove > FS {a, a} = FS {a}. > > In which case, what do we make of FS {a, a} ->asBag? Haven't we > irrevocably lost the fact that there were 2 a's as soon as we make it a FS? True. Any conversion of any kind of Set into a Bag ends up with just 1 of each. If you want an association to represent a Bag, you write {Bag} against it; and you get an ordinary Bag. There may be an argument for using FlatBags instead of FlatSets, but I think that's separate from the issue of whether we get the behaviour we want by definition of "." or by defining the behaviour of the type. Alan


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