I have a problem understanding a definition at page 93 of 'from perturbative to constructive renormalization', that is related to Graph Theory, and he uses it on the proof of the uniform BPH theorem for [itex]\phi_4^4[/itex] ([itex]\lambda \phi^4[/itex] in [itex]D=4[/itex]). You have a graph G, a forest of quadrupeds F, and g a subgraph of G compatible with the tree structure of F. [itex]B_F(g)[/itex] is defined as the ancestor of g in FUG. What means ancestor in this context? Maybe this question doesn't belong here, I'm sorry if that's the case. I thought that it belonged here because it's related to renormalization.