presto-main/src/main/java/io/prestosql/sql/planner/optimizations/AddExchanges.java/AddExchanges/createDirectTranslator
class AddExchanges:        private <T> Function<T, T> createDirectTranslator(SetMultimap<T, T> inputToOutput)
        {
            return input -> inputToOutput.get(input).iterator().next();
        }