Fig. 1. Two equally likely kinds of crossovers are considered: at non-ring (a–c) and at ring positions (d–f). Two equally likely kinds of ring cuts are considered: adjacent bonds and bonds separated by one bond. For ring crossovers fragments can be mated using both single and double bonds. (c) and (e) each shows two examples of children made by the mating process. Methylflouride is discarded because it is too small and the cycloheptene ring is discarded because the ring is too large.