sets of sets

From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 30 Jul 2006 17:36:06 GMT
Message-ID: <a66zg.277513$Mn5.253389_at_pd7tw3no>



I'm trying to read a recent paper I found at http://csr.uvic.ca/~vanemden/Publications/STPCS.pdf

(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".

Below I've tried to paste the pdf text, not sure how it will show up in different newsreaders, sorry for breaking the rules with a little bit of non-text:

Let S be a nonempty set of sets. Then ∪S is defined as {x | ∃S′ ∈ S . x ∈ S′} ...

Then he mentions what I call "INTERSECTION S" which seems to mean the set of x such that x is a member of all subsets of S", (text pasted below, I hope):

and ∩S as {x | ∀S′ ∈ S . x ∈ S′}.

p Received on Sun Jul 30 2006 - 19:36:06 CEST

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