# MAA

## Seminar

### Approximation in difference valuation rings

Seminar Room 1, Newton Institute

#### Abstract

I will discuss a result analogous to a theorem of Greenberg on an approximation property in henselian discrete valuation rings, but for polynomial equations involving also a fixed automorphism. In the case of Witt vectors and their Frobenius, a nullstellensatz for these equations can be deduced.