presto-main/src/main/java/io/prestosql/sql/planner/plan/TopNNode.java/TopNNode/replaceChildren
class TopNNode:    @Override
    public PlanNode replaceChildren(List<PlanNode> newChildren)
    {
        return new TopNNode(getId(), Iterables.getOnlyElement(newChildren), count, orderingScheme, step);
    }