presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PropertyDerivations.java/PropertyDerivations/exchangeInputToOutput
class PropertyDerivations:        public static Map<Symbol, Symbol> exchangeInputToOutput(ExchangeNode node, int sourceIndex)
        {
            List<Symbol> inputSymbols = node.getInputs().get(sourceIndex);
            Map<Symbol, Symbol> inputToOutput = new HashMap<>();
            for (int i = 0; i < node.getOutputSymbols().size(); i++) {
                inputToOutput.put(inputSymbols.get(i), node.getOutputSymbols().get(i));
            }
            return inputToOutput;
        }