Semi-Cartesian squares and the Snake Lemma
arXiv:1712.01637
Abstract
The well-known snake lemma is proved entirely within category theory, without the help of "points with value in..." à la Grothendieck, nor pseudo-elements as in Guglielmetti & Zaganidis. Instead, we define and use consistently semi-cartesian squares, which were promoted by C. Chevalley.
8 pages, self-contained