presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/Rewriter/rewriteSources
class Rewriter:        private static ImmutableList.Builder<PlanNode> rewriteSources(SetOperationNode node, RewriteContext<Void> context)
        {
            ImmutableList.Builder<PlanNode> rewrittenSources = ImmutableList.builder();
            for (PlanNode source : node.getSources()) {
                rewrittenSources.add(context.rewrite(source));
            }
            return rewrittenSources;
        }