Characteristic Function of Limit Superior of Sequence of Sets

Theorem
Let $\sequence {E_n}_{n \mathop \in \N}$ be a sequence of sets.

Let $E := \ds \limsup_{n \mathop \to \infty} E_n$ be the limit superior of the $E_n$.

Then:


 * $\ds \chi_E = \limsup_{n \mathop \to \infty} \chi_{E_n}$

where:


 * $\chi$ denotes characteristic function
 * $\ds \liminf_{n \mathop \to \infty} \chi_{E_n}$ is the pointwise limit superior of the $\chi_{E_n}$