2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/140643We enumerate the intervals in the Tamari lattices. For this, we introduce an inductive description of the intervals. Then a notion of "new interval" is defined and these are also enumerated. A a side result, the inverse of two special series is computed in a group of tree-indexed series.17 pages, 5 figuresCombinatorics05A15, 06A20text