Monoid Kernels and Profinite Topologies on the Free Abelian Group

On Profinite Uniform Structures Defined by Varieties of Finite Monoids

This paper arose during the preparation of [11], a paper on pro-p topologies extending the results of [12]. After recollecting various assertions on profinite topologies, we tried to improve existing statements and to arrange our notes into a readable form. We soon realized that many results were spread out in the literature, some of them not being stated in the way we wished and some other one...

Rational Codes and Free Profinite Monoids

It is well known that clopen subgroups of finitely generated free profinite groups are again finitely generated free profinite groups. Clopen submonoids of free profinite monoids need not be finitely generated nor free. Margolis, Sapir and Weil proved that the closed submonoid generated by a finite code (which is in fact clopen) is a free profinite monoid generated by that code. In this note we...

Maximal abelian subgroups of free profinite groups

THEOREM. Let F be the free profinite group on a set X, where \X\ > 2, and let n be a non-empty set of primes. Then F has a maximal abelian subgroup isomorphic to HpEn Zp. The idea of the proof is the following: we show that A — Ylpe7I1p is a free factor of Pa, i.e. fia ^ A *B for some profinite group B. To conclude from this that A is a maximal abelian subgroup of Fa (the general case then foll...

Profinite Topologies in Free Products of Groups

Let H be an abstract group and let C be a variety of finite groups (i.e., a class of finite groups closed under taking subgroups, quotients and finite direct products); for example the variety of all finite p-groups, for a fixed prime p. Consider the smallest topology on H such that all the homomorphism H −→ C from H to any group C ∈ C (endowed with the discrete topology) is continuous. We refe...

Inverse Automata and Profinite Topologies on a Free Group