2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53840The vanishing of the anomaly in the recent example of Nappi and Witten, constructed from the Wess-Zumino-Witten model based on a certain non-semisimple group, follows from a more general result valid for gravitational waves. The construction of the metric is explained.}High Energy Physics - Theorytext