What does this symbol mean? (looks like a 1 with double vertical line) I'm studying a course on probability and statistics and at some point this symbol comes up without introduction. It looks like the number one, but slightly bigger and with a double vertical line.
First time it comes up is when discussing stochastic/random variables that are neither continuous nor discreet in an example:

And somewhat later in a proof:

Anyone got an idea what this symbol represents?
EDIT: Thanks for the fast answers, I was still editing the question for better (larger) images :)

It's the indicator function, you can write $\chi_A(x)=\begin{cases}1, & x\in A\\0, & x\notin A\end{cases}$ instead. It's easier in $\text{LaTeX}$ and everybody knows that you mean the indicator function.
