2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/152079We discuss Ghys' theorem on 4 zeroes of the Schwarzian derivative and its relation with flattening points of Legendrian curves and Sturm theory.14 pages, 7 postscript figures, anonymous ftp at ftp://cpt.univ-mrs.fr/ or gopher://cpt.univ-mrs.fr/Differential Geometrytext