presto-main/src/main/java/io/prestosql/sql/planner/optimizations/AddExchanges.java/Rewriter/createTranslator
class Rewriter:        private <T> Function<T, Optional<T>> createTranslator(SetMultimap<T, T> inputToOutput)
        {
            return input -> inputToOutput.get(input).stream().findAny();
        }