Figure 1

A phylogenetic tree and a restricted subtree. (a) shows a tree T witnessing that the quartets q ₁ =ab|ce, q ₂ =cd|bf, and q ₃ =ad|ef are compatible; T is also a witness that the characters ${\mathit{\chi }}_{{\mathit{q}}_{\mathbf{1}}}=\mathit{ab}\left|\mathit{\text{ce}}\right|d|f$, ${\mathit{\chi }}_{{\mathit{q}}_{\mathbf{2}}}=\mathit{cd}\left|\mathit{\text{bf}}\right|a|e$, and ${\mathit{\chi }}_{{\mathit{q}}_{\mathbf{3}}}=\mathit{ad}\left|\mathit{\text{ef}}\right|b|c$ are compatible; (b) shows T|{a,b,c,d,e}.