# On the class $A=\{x\mid x\text{ is not an element of }x\}$ [duplicate]

Possible Duplicate:
The set of all sets of the universe?

What's the ideas in here?

In my opinion, "is an element of" or "is not an element of" is kind a things using in the concept about set, and If $x$ is a set, than it do means $\{Y\}$ is not an element of $Y=\{B, C, D, E\}$.

The question I'm confusing:

$A=\{x\mid x\text{ is not an element of }x\}$ // I don't even understand the definition

1. $A$ is not an element of $A$ if $A$ is an element of $A$
2. $A$ is an element of $A$ if $A$ is not an element of $A$
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