Linking the Calkin–Wilf and Stern–Brocot trees

Links between the Calkin–Wilf tree and the Stern–Brocot tree are discussed answering the questions: What is the  jjth vertex in the  nnth level of the Calkin–Wilf tree? and Where is the vertex  rslocated in the Calkin–Wilf tree?   A simple mechanism is described for converting the jjth vertex in the nnth level of the Calkin–Wilf tree into the jjth entry in the nnth level of the Stern–Brocot tree. We also provide a simple method for evaluating terms in the Hyperbinary sequence thus answering a challenge raised in Quantum in September 1997. We also examine successors and predecessors in both trees.