John J. O’Connor; Edmund F. Robertson: Édouard Goursat w MacTutor History of Mathematics archive(ang.): It is almost certain that l’Hôpital’s rule, for finding the limit of a rational function whose numerator and denominator tend to zero at a point, is so named because Goursat named the rule after de l’Hôpital in his Cours d’analyse mathématique. Certainly the rule appears in earlier texts (for example it appears in the work of Euler), but Goursat is the first to attach de l'Hôpital's name to it.