Is $a\in[a,a)$?

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The title is my question, no more things.

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$[a,b)$ is defined as $\{x:\ a\leq x < b\}$. If $a=b$ then the inequality $a\leq x < a$ is never satisfied. Therefore the set is empty.

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No, as $[a,a)$ means $a \le a $ and $a<a$ according to Baby Rudin. The second inequality is clearly false, so the set $[a,a)=\varnothing$.