How to represent sections in math notation? E.g. (_ + 3)

Question

Functional programming languages have the concept of sections where they can partially apply a function that is represented by an operator. For instance, one can define a function that always adds three to its argument $f(x) =x+3$ and use it $f(2)$, or avoid having to define the function/argument just by using sections : $(\_ + 3)$. Some contrived use would be $(\_ + 3)(2)$. Is this _ notation currently known in academic math texts?

Answer 1

You can use Lambda calculus. For your example we could write the function application as $$(x\mapsto x+3)(2)=2+3=5$$