# Nottingham group

The subgroup of automorphisms of the field of formal power series $\mathbf{F_p}[[t]]$ consisting of those automorphisms of the form $f(t) \mapsto f(g(t))$ where $g(t) \in t + O(t^2)$.
It is a finitely generated, just infinite pro-$p$ group of finite width. However, every separable pro-$p$ group can be embedded in it as a closed subgroup.