Published online by Cambridge University Press: 11 January 2022
Given a fixed graph H that embeds in a surface $\Sigma$, what is the maximum number of copies of H in an n-vertex graph G that embeds in
$\Sigma$? We show that the answer is
$\Theta(n^{f(H)})$, where f(H) is a graph invariant called the ‘flap-number’ of H, which is independent of
$\Sigma$. This simultaneously answers two open problems posed by Eppstein ((1993) J. Graph Theory 17(3) 409–416.). The same proof also answers the question for minor-closed classes. That is, if H is a
$K_{3,t}$ minor-free graph, then the maximum number of copies of H in an n-vertex
$K_{3,t}$ minor-free graph G is
$\Theta(n^{f'(H)})$, where f′(H) is a graph invariant closely related to the flap-number of H. Finally, when H is a complete graph we give more precise answers.
All three authors are supported by the Australian Research Council. G. Joret is supported by an ARC grant from the Wallonia-Brussels Federation of Belgium and a CDR grant from the National Fund for Scientific Research (FNRS).