2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/47390HQET lagrangian up to $1/m^3$ terms is discussed. Consequences of reparameterization invariance are considered. Results for the chromomagnetic interaction coefficient at two loops, and in all orders in the large--$β_1$ approximation, are presented.LaTeX2e, 13 pages, figures included; Invited plenary talk at the IV Int. Workshop on Progress in Heavy Quark Physics, Rostock, September 20-22High Energy Physics - Phenomenologytext