Tree S ( V ) for a fixed partition V = V
. Here V, V1, V2 designates both the corresponding vertex and the edge upwards from this vertex. Trees S(V1) and S(V2), as well as their costs c(V1) and c(V2), are already known from induction, and C
corresponds to evolutionary events in edges of V, V1, V2. Those are not known from induction and should be computed separately, as defined below in the text.