Profinite groups in which the probabilistic zeta function has no negative coefficients

To a finitely generated profinite group [Formula: see text], a formal Dirichlet series [Formula: see text] is associated, where [Formula: see text] and [Formula: see text] denotes the Möbius function of the lattice of open subgroups of [Formula: see text] Its formal inverse [Formula: see text] is the probabilistic zeta function of [Formula: see text]. When [Formula: see text] is prosoluble, every coefficient of [Formula: see text] is nonnegative. In this paper we discuss the general case and we produce a non-prosoluble finitely generated group with the same property.

Center cyclicity for some nilpotent singularities including the ℤ2-equivariant class

This work concerns with polynomial families of real planar vector fields having a monodromic nilpotent singularity. The families considered are those for which the centers are characterized by the existence of a formal inverse integrating factor vanishing at the singularity with a leading term of minimum [Formula: see text]-quasihomogeneous weighted degree, being [Formula: see text] the Andreev number of the singularity. These families strictly include the case [Formula: see text] and also the [Formula: see text]-equivariant families. In some cases for such families we solve, under additional assumptions, the local Hilbert 16th problem giving global bounds on the maximum number of limit cycles that can bifurcate from the singularity under perturbations within the family. Several examples are given.

Nilpotent centres via inverse integrating factors

In this paper, we are interested in the nilpotent centre problem of planar analytic monodromic vector fields. It is known that the formal integrability is not enough to characterize such centres. More general objects are considered as the formal inverse integrating factors. However, the existence of a formal inverse integrating factor is not sufficient to describe all the nilpotent centres. For the family studied in this paper, it is enough.

Formal Inverse Integrating Factor and the Nilpotent Center Problem

We are interested in deepening the knowledge of methods based on formal power series applied to the nilpotent center problem of planar local analytic monodromic vector fields [Formula: see text]. As formal integrability is not enough to characterize such a center we use a more general object, namely, formal inverse integrating factors [Formula: see text] of [Formula: see text]. Although by the existence of [Formula: see text] it is not possible to describe all nilpotent centers strata, we simplify, improve and also extend previous results on the relationship between these concepts. We use in the performed analysis the so-called Andreev number [Formula: see text] with [Formula: see text] associated to [Formula: see text] which is invariant under orbital equivalency of [Formula: see text]. Besides the leading terms in the [Formula: see text]-quasihomogeneous expansions that [Formula: see text] can have, we also prove the following: (i) If [Formula: see text] is even and there exists [Formula: see text] then [Formula: see text] has a center; (ii) if [Formula: see text], the existence of [Formula: see text] characterizes all the centers; (iii) if there is a [Formula: see text] with minimum “vanishing multiplicity” at the singularity then, generically, [Formula: see text] has a center.

The stereoselective formation of highly substituted CF3-dihydropyrans as versatile building blocks

The dienamine-mediated formal inverse electron demand hetero Diels–Alder reaction providing optically active 5-bromo-6-(trifluoromethyl)-3,4-dihydro-2H-pyrans is disclosed along with interesting transformations, affording a large variety of fully substituted dihydropyrans.