January 2024
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Revista Colombiana de Matemáticas
In his celebrated article of 1956, John Milnor established the existence of smooth structures on the 7-dimensional sphere that differs from the usual one. These so-called "exotic" structures have been of great interest ever since. The purpose of this article is to give a clear exposition of the different tools that Milnor used in order to provide an almost self-contained construction of exotic structures on the 7-dimensional sphere and then to show that they are not diffeomorphic to the standard sphere.