https://drive.google.com/drive/folders/0B6WDPDeJDzt5fjl5SHFuc0l2U21VMk1uYk1KZ0xFbUw0aktsanpPWFBXTGZzekFqRjJyd0E
(the first lecture)
and slide 2 of
https://docs.google.com/document/d/1dXqShlLpi6tzzGE04wx23KRRNEQ4CkSuMsmjxTznbLc (the second lecture)