Function sub

sub(firstExpression, secondExpression): OGCCondition
Creates a subtraction OGC expression. It takes two parameters, each one being an OGC expression.

Note that arithmetic operators are no longer supported in OGC Filter 2.0. You will get an error when you use them in OGC Filter 2.0 XML (for example WFS 2.0). You can still create them, evaluate them and use them in OGC Filter 1.1 XML though.
```
  FilterFactory.sub(
    FilterFactory.property("age")
    FilterFactory.literal(18),
  );
```
Parameters
- firstExpression: Expression
  the first expression
- secondExpression: Expression
  the second expression
Returns OGCCondition
BinaryOperator

Throws
Error if not all parameters are OGCExpression