// Summing the sliding windows with gatherers
var strings = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9);
Gatherer<Integer, ?, List<Integer>> createSlidingWindows =
        Gatherers.windowSliding(2);
Gatherer<List<Integer>, ?, Integer> sumEachWindow =
        Gatherer.of((_, list, downstream) -> downstream.push(list.stream().mapToInt(n -> n).sum()));
var result = strings.stream()
        .gather(createSlidingWindows)
        .gather(sumEachWindow)
        .toList();
System.out.println("result = " + result);