private static long size(final int n, final int k) {
		try {
			return BinomialCoefficient.apply(n, k);
		} catch (ArithmeticException e) {
			throw new IllegalArgumentException(
				"KSubset[" + "n=" + n + ", " + "k=" + k + ']' + " to big."
			);
		}
	}
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