This operator adds cumul function expression f to the invoking cumul function expression.

This method must be implemented so that it copies the invoking object to the engine of the given copy manager using the copy manager.

This operator subtracts cumul function expression f from the invoking cumul function expression.

This method is called when the object and all its sub-objects must be visited. To implement this method, you should first call the method ICopyableVisitor.BeginVisit() with yourself as parameter, then call ICopyableVisitor.VisitChild() for each sub-copyables, the call ICopyableVisitor.EndVisit() once again with yourself as parameter.