presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PlanNodeDecorrelator.java/PlanNodeDecorrelator/visitGroupReference
class PlanNodeDecorrelator:        @Override
        public Optional<DecorrelationResult> visitGroupReference(GroupReference node, Void context)
        {
            return lookup.resolve(node).accept(this, null);
        }