elements of nested sets I was thinking about elements of the power set, and I know that for a power set $P=\{\{\},\{a\},\{b\},\{a,b\}\}$ that $\{\},\{a\},\{b\},\{a,b\}$ are all elements of $P$. However, if you have another set containing sets, such as $A=\{1, 2, \{3, 4\}\}$: is 3 an element of $A$?
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