presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/Rewriter/canonicalizeExchangeNodeInputs
class Rewriter:        private List<Symbol> canonicalizeExchangeNodeInputs(ExchangeNode node, int symbolIndex)
        {
            return node.getInputs().stream()
                    .map(input -> canonicalize(input.get(symbolIndex)))
                    .collect(toImmutableList());
        }