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. 2011 Nov;18(11):1543–1559. doi: 10.1089/cmb.2011.0174

FIG. 2.

FIG. 2.

Under the coalescent, time flows backward from the leaves towards the root. In a valid coalescent history, the number of lineages in edge e = (u, v) equals the sum of the numbers of lineages entering e, when going backward in time, from edges (v, x) and (v, y), minus the number of coalescence events that occur at node v.