Algebraic Topology - 3 - Using a Functor to Prove the Disc Doesn't Retract to a Circle

In this video we explain how we can prove that there is no retraction from the disc to its boundary. The idea is to assume that a retraction does exist and then derive a contradiction by the way the fundamental group behaves.

[beback_]

Absolutely love your presentation style. Also this format with you writing on paper and yourself in the background is more engaging that the tablet-based one in your Model Theory course.

[narutosaga]

Wait why is the 3rd video up and there was no 2nd lecture video? Is there a reason we went from 1 to 3?