The Mathematics Days (X-UPS) are a training course, held every year in the spring, organized by the Centre de mathématiques Laurent Schwartz at the École polytechnique for mathematics teachers of preparatory classes for the `Grandes Écoles'. The aim is twofold: to satisfy teachers' interest in current research in mathematics, and to provide them with knowledge that can be used in their teaching. The course includes in general six lectures given by three lecturers on the same topic, in fundamental or applied mathematics.
Since the late 1990s, the texts have been published by Éditions de l'École polytechnique as an annual printed volume. An electronic version of these texts is simultaneously available. From Journées 2023 onwards, this electronic version is available on the Centre Mersenne website, which also offers a re-edition of the electronic version of the texts from 1991 to 2022, published in August 2024. This re-edition introduces a table of contents for each text, updates the bibliography and improves navigation in the pdf file. As a result, the pagination differs slightly from that of the original version.