Fig 1. 3-way edges and intersections.

(a) A small, 3-way network consisting of 5 nodes v ₁, v ₂, v ₃, v ₄ and v ₅ and two 3-way edges e ₁ and e ₂. Edge e ₁ connects nodes v ₃, v ₄ and v ₅ and edge e ₂ connects nodes v ₁, v ₂ and v ₃. (b) Venn diagram for a 3-way intersection of species. a is the number of families present in species A, b is the number of families present in species B, c is the number of families present in species C, ab is the number of families present in species A and species B, ac is the number of families present in species A and species C, bc is the number of families present in species B and species C, abc is the number of families present in species A, B and C, $\bar{a}$ is the number of families present only in species A, $\bar{b}$ is the number of families present only in species B and $\bar{c}$ is the number of families present only in species C.