2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/71064A book of size $q$ is a set of $q$ triangles sharing a common edge. We study the size of the maximal book in a graph as a function of the number of its edges. In particular, we answer two questions of Erdos about graphs that are union of triangles.13 pages, accepted in Eur. J. CombinCombinatorics05C35text