MathType - The indicator function of the rational numbers is also known as Dirichlet function. Dirichlet was the first to study this types of functions, which are nowhere continuous #Analysis #MathType | Facebook
Characteristic Function -- from Wolfram MathWorld
Characteristic Function -- from Wolfram MathWorld
Indicator function - Wikipedia
ḹ | latin small letter l with dot below and macron | Times New Roman, Regular @ Graphemica
How to model the indicator function in Gurobi – Gurobi Help Center