#### Alladi Ramakrishnan Hall

#### Groups of power series under substitution and automorphisms of curves.

#### Peter Symonds

##### University of Manchester

*It is known that the group formed by formal power series over a field of characteristic p with no constant term under substitution contains every finite p-group, but it is very hard to realise these finite subgroups explicitly. We discuss this problem and show how it is related to group actions on curves. Using this connection, we can construct an explicit element of order 4; no such construction was known before.*

Done