Another common optimization is employment of "unary change accumulation" and "batch propagation". Such a solution can be faster because it reduces communication among involved nodes. Optimization strategies can then be employed that reason about the nature of the changes contained within, and make alterations accordingly. e.g. two changes in the batch can cancel each other, and thus, simply be ignored. Yet another available approach, is described as "invalidity notification propagation". This approach causes nodes with invalid input to pull updates, thus resulting in the update of their own outputs.