How to use [math.increment]

The reference page of math.increment has its arguments, constraints and declaration.

This slot increments the value of some expression in place, by mutating the value of the node its expression is leading to.

.arg:int:5
math.increment:x:@.arg

It can optionally be given a [step] argument, such as illustrated below.

.arg:int:5
math.increment:x:@.arg
   .:int:2