Explore the fourth lecture in the Topology series of the Minicourse on Partial Differential Equations: Analytical and Numerical Tools, delivered by Oscar Reula from the National University of Córdoba, Argentina. This 37-minute video continues the exploration of topological concepts as they relate to partial differential equations, building upon the foundation established in previous classes. The lecture is part of a comprehensive program organized by ICTP-SAIFR, scheduled to run from May 5 to June 30, 2025. Gain valuable insights into advanced mathematical concepts and their applications in solving complex differential equations through analytical and numerical approaches.