presto-main/src/main/java/io/prestosql/operator/scalar/ArrayCombinationsFunction.java/ArrayCombinationsFunction/firstCombination
class ArrayCombinationsFunction:    private static int[] firstCombination(int arrayLength, int combinationLength)
    {
        int[] combination = new int[combinationLength + 1];
        setAll(combination, i -> i);
        combination[combinationLength] = arrayLength; // sentinel
        return combination;
    }