presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/TransformCorrelatedInPredicateToJoin.java/TransformCorrelatedInPredicateToJoin/visitPlan
class TransformCorrelatedInPredicateToJoin:        @Override
        protected Optional<Decorrelated> visitPlan(PlanNode node, PlanNode reference)
        {
            if (isCorrelatedRecursively(node)) {
                return Optional.empty();
            }
            else {
                return Optional.of(new Decorrelated(ImmutableList.of(), reference));
            }
        }