(a) A host tree with three different timings shown in (b), (c), and (d). The numbers underneath each timing indicate the relative time of each vertex in that timing. The timings in (c) and (d) differ only in the relative times of nodes b and c, two nodes that occur at consecutive relative times but such that neither is the parent of the other. Thus, these two timings are said to be neighbors.
Conow et al. Algorithms for Molecular Biology 2010 5:16 doi:10.1186/1748-7188-5-16