presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/UnaliasSymbolReferences/visitOutput
class UnaliasSymbolReferences:        @Override
        public PlanNode visitOutput(OutputNode node, RewriteContext<Void> context)
        {
            PlanNode source = context.rewrite(node.getSource());

            List<Symbol> canonical = Lists.transform(node.getOutputSymbols(), this::canonicalize);
            return new OutputNode(node.getId(), source, node.getColumnNames(), canonical);
        }