文摘
In this short note, we explain how one can prove without projective tools that the higher direct images of a coherent sheaf under a map between two schemes of finite type over a field are coherent. The proof consists in endowing the ground field with the trivial absolute value and using the corresponding finiteness theorem for Berkovich spaces (after having proven at hand a suitable GAGA-principle). The latter theorem comes itself from a theorem of Kiehl in rigid geometry, whose proof is based upon the theory of completely continuous maps between p-adic Banach spaces (in the spirit of Cartan and Serre’s proof of the finiteness of coherent cohomology on a compact complex analytic space).