Seventh lesson (February 20, 2012), based on the first 4 sections of chapter 9 of "Algorithmic Game Theory" edited by Noam Nisan, Tim Roughgarden, Éva Tardos, Vijay V. Vazirani, Cambridge University Press. In particular the first 3 sections have been explained in detail (skipping Arrow Theorem). About section 4 only the revelation principle has been stated. A non printable version of the whole book is available here. A printable version of chapter 9 (but with wrong numbering) is downloadable here here.