2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/187191The tools of presymplectic geometry are used to study light rays trajectories in anisotropic media.LaTeX file, no figures. To appear in J. Phys. A: Math. and GenHigh Energy Physics - TheoryDifferential GeometryPresymplectic Geometry and Fermat's Principle for anisotropic mediatext