private static Subset end(final int n, final int k) {
		final var a = new int[k];
		for (int i = n - k; i < n; ++i) {
			a[i - n + k] = i;
		}
		return new Subset(a);
	}
Create a new k-subset object with the given {@code n} and {@code k}.

@throws IllegalArgumentException if {@code n < 0 || n < k} or
        {@code binomial(n, k) > Long.MAX_VALUE}
jenetics.incubator/src/main/java/io/jenetics/incubator/combinatorial/KSubset.java