Cartan's theorem

Cartan's theorem refers to various results in differential geometry and related fields that are associated with the mathematician Henri Cartan. The most notable of these results include: 1. **Cartan's Theorems A and B:** These theorems are fundamental results in the theory of differential equations and are particularly important in the study of systems of partial differential equations. They relate to the integrability of differential forms and the existence of solutions to certain types of differential equations.