public interface CombineAggregator<K, V, VA> extends Aggregator<KCombinator<K, V, VA> {

        VA combine(final VA agg1, final VA agg2);
}

<VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                             final Aggregator<? super K, ? super V, VR> aggregator,
                             final Combinator<? super K, VR, VR> combinator);

<VR> KTable<K, VR> aggregate(final Initializer<VR> initializer,
                             final Aggregator<? super K, ? super V, VR> aggregator,
                             final Combinator<? super K, VR, VR> combinator,
                             final Combinator<? super K, VR, VR> inverter);