Math 139 050225 Dirichlet's Theorem Part IV: L(1,X) nonzero for nontrivial real Dirichlet characters

From a channel Lumen includes in full: Winston Ou, a university maths professor, posts full recorded class sessions of his courses in real analysis and algebra.

A 46-minute video from Winston Ou's catalogue; the title names its topic.

Video by Winston Ou, played through YouTube's embedded player.