`X`

represents the name and arity of the predicate. `Y`

represents the full class name of an implementation of `org.projog.core.ArithmeticOperator`

.

### Examples

` ?- X is sum(1, 1).`

Cannot find arithmetic operator: sum/2

?- pj_add_arithmetic_operator(sum/2, 'org.projog.core.math.builtin.Add').

yes

?- X is sum(1, 1).

X = 2

yes