presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PlanNodeDecorrelator.java/PlanNodeDecorrelator/decorrelatedNode
class PlanNodeDecorrelator:    private Optional<DecorrelatedNode> decorrelatedNode(
            List<Expression> correlatedPredicates,
            PlanNode node,
            List<Symbol> correlation)
    {
        if (containsCorrelation(node, correlation)) {
            // node is still correlated ; /
            return Optional.empty();
        }
        return Optional.of(new DecorrelatedNode(correlatedPredicates, node));
    }