presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/SingleDistinctAggregationToGroupBy.java/SingleDistinctAggregationToGroupBy/extractArgumentSets
class SingleDistinctAggregationToGroupBy:    private static Stream<Set<Expression>> extractArgumentSets(AggregationNode aggregationNode)
    {
        return aggregationNode.getAggregations()
                .values().stream()
                .filter(Aggregation::isDistinct)
                .map(Aggregation::getArguments)
                .<Set<Expression>>map(HashSet::new)
                .distinct();
    }