A question about interpreting a Set Notation that describes Petri-Net properties

Question

I have a set notation from a particular paper about Petri-Nets, that I have read.

$$\mathbf{1}_F( (p,\rho(e)) ) = |\rho^{-1} (p) ∩ ● e|$$

Where $F \subseteq (P \times T) \cup (T \times P)$ and $p \in P$

In general terms, what is $\mathbf{1}_F$?

Answer 1

I missed it: this is the indicator function: $$\mathbf{1}_F(x) = \begin{cases} 1\ ,\ x\in F\\ 0\ ,\ x\notin F \end{cases}$$

It looks like this is a common notation; I am a bit more familiar with another notation $\chi_F$.