Figure 2

Propagation rules. Propagation rules for an adjacency ab: a function of the events happening to its extremities a and b (events happening to a are written on the left, events happening to b are written on the right). If a₁, a₂, b₁ and b₂ are the children of a and b. Numbers on each subsquare are recurrence rules following the propagation rule. Recurrence rules add the possibility of rearrangements at each step. For combination of duplication or loss with another event not mentioned here, follow the rule with "no event" (the duplication or loss is supposed to happen first).