I always struggle to write an indicator function in Latex. You know, the 1 with a double bar, for instance in π_A(x). For letters like N, a simple \mathbb{N} gives a nice β, but \mathbb{1} gives a weird looking character that is definitely not a double-struck 1.
The best way I found is to import the dsfont package and use \mathds{1}:
\usepackage{dsfont}
\mathds{1}
It’s also possible to import the bbm package and use \mathbbm{1}, but I don’t recommend this option as it uses a bitmapped font for the π character. This kind of Type 3 fonts are not scalable and can cause formatting issues in some PDF checkers.