Audio narration (with digital pointer) to go with Slide 37 of G14FTA where the original recording failed.
Brief discussion of how to generate a topology from a collection of sets (as a sub-base), and how it is harder to give such a concrete approach to generating a σ-algebra. The intersection of any family of σ-algebras on X is still a σ-algebra on X. The definition of the σ-algebra on a set X generated by a collection of subsets of X. Brief discussion relating this to open sets and sets with the Property of Baire.