Lecture
This lecture presents the proof of the Seifert van Kampen theorem, focusing on a diagram involving spaces X, A, B, and C, and the homomorphisms induced by continuous maps. The theorem states that the induced application is an isomorphism, connecting the free product of fundamental groups of A and B with the fundamental group of X. The instructor explains the relationship between different homomorphisms and demonstrates that one of them is indeed an isomorphism, using a three-dimensional diagram to illustrate the concept.