A group is finitely axiomatizable (FA) in a class C if it can be determined up to isomorphism within by sentence the first-order language of theory. We show that profinite groups various kinds are FA groups, or pro- p for some prime p. Both algebraic and model-theoretic methods developed purpose. Reasons why certain cannot also discussed.

We study equivariant sheaves over profinite spaces, where the group is also taken to be profinite. resolve a serious deficit in existing theory by constructing good notion of presheaves, with suitable sheafification functor. Using sheafification, we develop general modules ring, give explicit constructions infinite products and introduce an analogue skyscraper sheaves. These results underlie re...

We initiate the study of the class of profinite graphs Γ defined by the following geometric property: for any two vertices v and w of Γ, there is a (unique) smallest connected profinite subgraph of Γ containing them; such graphs are called tree-like. Profinite trees in the sense of Gildenhuys and Ribes are tree-like, but the converse is not true. A profinite group is then said to be dendral if ...