2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/60463The purpose of this note is to correct an error in a paper of M. Cowling, G. Fendler and J.J.F. Fournier, and to give a counterexample to a conjecture of J.-L. Rubio de Francia.3 pages, no figures; submitted to Math AnnalenClassical Analysis and ODEs42A45text