Before I get on with my question, I'll have to make it clear that the only set theory I've encountered can be found in the first few pages of a high-school or college-level book.(adsbygoogle = window.adsbygoogle || []).push({});

Now, let me come to the question. Looking for a mathematical explanation of the source of Russell's paradox, I went to this page: http://planetmath.org/encyclopedia/RussellsParadox.html [Broken]

I came across this -> [tex]S = \left\{x:x\notin x \right\}[/tex]. If I read the notation correctly, it says, let S be a set of all x,such that x does not belong to/is not a member of x. What exactly does that mean? How can an element of a set belong or, in this case, not belong to itself?

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# [Russell's Paradox] Help with Notation

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