I don't think this is a fair critisim - they've just said it reverse order. They should start with the set of real numbers, denoted R, and then this can be spl

I don't think this is a fair critisim - they've just said it reverse order. They should start with the set of real numbers, denoted R, and then this can be split into two disjoint subsets - the rational numbers and the irrational numbers. From there the natural numbers are a subet of the rational numbers.