Lecture
This lecture introduces the concept of isomorphism in categories, defining a morphism as an isomorphism if it has an inverse. Objects a and b are considered isomorphic if there exists a morphism g: b → a such that gof = Ida and fog = Idb. An automorphism is an isomorphism with equal domain and codomain, while a groupoid consists of categories where all morphisms are isomorphisms. The lecture also covers examples of categories and hints at the next topic: functors.