Notes on the Atiyah-Singer Index Theorem by Liviu I. Nicolaescu
Publisher: University of Notre Dame 2005
Number of pages: 135
This is arguably one of the deepest and most beautiful results in modern geometry, and it is surely a must know for any geometer / topologist. It has to do with elliptic partial differential operators on a compact manifold.
Mathematics Geometry & Topology Differential Geometry