On the Alexander–Hirschowitz theorem

The Alexander–Hirschowitz theorem says that a general collection of kk double points in Pn imposes independent conditions on homogeneous polynomials of degree dd with a well-known list of exceptions. Alexander and Hirschowitz completed its proof in 1995, solving a long standing classical problem, connected with the Waring problem for polynomials. We expose a self-contained proof based mainly on the previous works by Terracini, Hirschowitz, Alexander and Chandler, with a few simplifications. We claim originality only in the case d=3d=3, where our proof is shorter. We end with an account of the history of the work on this problem.