The previous lecture in this series is here. The next lecture in this series is here.
We show that the Frobenius automorphism of a finite field an sometimes be lifted to characteristic 0. As an example we use the Frobenius automorphisms of ℚ[i] to prove that -1 is a square mod an odd prime p if and only if p is 1 mod 4.
This video is part of a lecture course by Richard Borcherds from 2020-21.