|→ indicates the corresponding relationship between independent variables and dependent variables.
For example, if F is the mapping from set A to set B, and any element A in A is replaced by f(a), then the expression is as follows:
F: A→B (there are only arrows here)
A|→f(a) (there is a vertical line here)
The reason why a short vertical line is added is to distinguish it from the above set of relationships.