The set S contains some real numbers, according to the following three rules. (i) 1 1 is in S. (ii) If a b is in S, where a b is written in lowest terms (that is, a and b have highest common factor 1), then b 2a is in S. (iii) If a b and c d are in S, where they are written in lowest terms, then a c b d is in S. These rules are exhaustive: if these rules do not imply that a number is in S, then that number is not in S. Can you describe which numbers are in S