a∈A
b∈A
u∈B
a∉B
b∉B
u∉A
\(\hept{\begin{cases}a\in A\\a\notin B\end{cases}}\) \(\hept{\begin{cases}b\in A\\b\in B\end{cases}}\) \(\hept{\begin{cases}u\notin A\\u\in B\end{cases}}\)
a ∈ A ; a ∉ B
b ∈ A ; b ∈ B
x ∈ A ; x ∉ B
u ∉ A ; u ∈ B
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