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Let$χ$be an analytic vector field defined in a real-analytic manifold of dimension three. We prove that all the singularities of$χ$can be made elementary by a finite number of blowing-ups in the ambient space.

A sufficient condition for the Wiener regularity of a boundary point with respect to the operator (− Δ)^{μ}in$R$^{$n$},$n$≥1, is obtained, for μ∈(0,1/2$n$)/(1,1/2$n$−1). This extends some results for the polyharmonic operator obtained by Maz'ya and Maz'ya-Donchev.

We study to what extent rearrangements preserve the integrability properties of higher order derivatives. It is well known that the second order derivatives of the rearrangement of a smooth function are not necessarily in$L$^{1}. We obtain a substitute for this fact. This is done by showing that the total curvature for the graph of the rearrangement of a function is bounded by the total curvature for the graph of the function itself.

Auslander–Reiten sequences are the central item of Auslander–Reiten theory, which is one of the most important techniques for the investigation of the structure of abelian categories.