reflective subcategories, Compactness, Convergence in general topology (sequences, filters, limits, convergence spaces, nets, etc.), Adjoint functors (universal constructions, reflective subcategories, Kan extensions, etc.), Categories of topological spaces and continuous mappings, Extensions of spaces (compactifications, supercompactifications, completions, etc.), coreflective subcategories, Čech-Stone compactification, Categorical methods in general topology