Calkin–Wilf tree

The Calkin-Wilf tree is a binary tree that provides a systematic way to enumerate all positive rational numbers (fractions) exactly once, ensuring that each fraction can be represented in its simplest form (i.e., with a numerator and denominator that share no common factors other than 1). This tree is named after mathematicians William Calkin and Herbert Wilf, who introduced the concept. ### Structure of the Calkin-Wilf Tree 1.