presto-main/src/main/java/io/prestosql/sql/analyzer/FreeLambdaReferenceExtractor.java/FreeLambdaReferenceExtractor/getFreeReferencesToLambdaArgument
class FreeLambdaReferenceExtractor:    public static List<Expression> getFreeReferencesToLambdaArgument(Node node, Analysis analysis)
    {
        Visitor visitor = new Visitor(analysis);
        visitor.process(node, ImmutableSet.of());
        return visitor.getFreeReferencesToLambdaArgument();
    }