Re: sets of sets

From: dawn <>
Date: 30 Jul 2006 12:15:46 -0700
Message-ID: <>

paul c wrote:
> I'm trying to read a recent paper I found at
> (The description intrigued me because the author is exploring RT. I'll
> try to contact the author with my question, but I thought I'd mention it
> here as others may be interested.)
> Anyway, at the top of page 5, he defines something I can only call
> "UNION S" (since I don't know know how to type the set union operator
> symbol).
> Can anybody suggest whether I'm reading it right? What I think it says
> in prose is "the set of x such that x is a member of some subset of S".

He says "Let S be a nonempty set of sets" (so you can think of S = {S1, S2, ... , Sn} where each Sm is a set. Then UnionS (US) is the set of all x such that there is an element of S (S' in his def would be one of those Sm's that are elements) where x is an element of that element of S. So, if you have

S = { {cat, dog}, {dog, bunny, pumpkin pie} } then US = {cat, dog, bunny, pumpkin pie}

nS (intersection S) = { dog }

HTH. Received on Sun Jul 30 2006 - 21:15:46 CEST

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