Florian Litzinger - Optimal regularity for Pfaffian systems and the fundamental theorem of surface theory

The fundamental theorem of surface theory asserts the existence of a surface immersion with prescribed first and second fundamental forms that satisfy the Gauss–Codazzi–Mainardi equations. Its proof is based on the solution of a Pfaffian system and an application of the Poincaré lemma. Consequently, the regularity of the resulting immersion crucially depends on the regularity of the solution of the corresponding Pfaffian system. This talk shall briefly review both the classical smooth case and the regularity theory and then introduce an extension to the optimal regularity.