In agreement with the main tenets of the anthropological theory of the didactic (ATD), this study uncovers dependencies between what students can learn, the established curriculum and the current state of mathematicians' mathematics ('scholarly mathematics'). One main result is that the mathematics taught, too often taken for granted by curriculum developers and teachers, is in fact problematic not only to students but also to teachers and curriculum developers and is sometimes a challenge even to current scholarly mathematics. The mathematics taught during a given historical period within a given institution contains flaws that, when they cease to go unnoticed, generate crises, in the form of breaches of the prevailing didactic contract. The resolution of these crises allows the institution and its actors--in particular students and teachers--to learn new contents and often also leads to the more or less damaging unlearning of old contents. This key phenomenon is illustrated, at the triple level of the classroom, the curriculum and scholarly mathematics, with regard to elementary algebra and mathematical analysis, most importantly in the case of maxima and minima problems.