2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/25860This is a comment inspired by recently published results [Y. Zhang et al., Phys. Rev. Lett. 91, 157404 (2003)] that introduced the name "amphoteric refraction" for the fact that at the interface with an optically anisotropic material there can be a range of incidence angles for which the component of the Poynting vector parallel to the interface changes sign upon refraction. The latter effect is a well-known consequence of optical anisotropy, but it was described as a new negative refraction phenomenon that can be put in the same class as the negative refraction observed at an interface with a left-handed material with negative refractive index.LaTeX/RevTeX, 2 pages, 2 figuresOther Condensed Mattertext