arXiv subjects
Publications and source records attributed to Małgorzata Michalska.
In this paper we investigate intertwining relations for compressions of $k^{th}$--order slant Toeplitz operators to model spaces. We then ask when a product of two such compressions is a compression itself.
We discuss de Branges-Rovnyak spaces $\mathcal H(b)$ generated by nonextreme and rational functions $b$ and local Dirichlet spaces of order $m$ introduced in [6]. In [6] the authors characterized nonextreme $b$ for which the operator $Y=S|_{\mathcal H(b)}$, the restriction of the shift operator $S$ on $H^2$ to $\mathcal H(b)$, is a strict $2m$-isometry and proved that such spaces $\mathcal H (b)$ are equal to local Dirichlet spaces of order $m$. Here we give a characterization of local Dirichlet spaces of order $m$ in terms of the $m$-th derivatives that is a generalization of a known result on local Dirichlet spaces. We also find explicit formulas for $b$ in the case when $\mathcal H(b)$ coincides with local Dirichlet space of order $m$ with equality of norms. Finally, we prove a property of wandering vectors of $Y$ analogous to the property of wandering vectors of the restriction of $S$ to harmonically weighted Dirichlet spaces obtained by D. Sarason in [11].
In this paper we consider compressions of $k^{th}$--order slant Toeplitz operators to the backward shift invariant subspaces of the classical Hardy space $H^2$. In particular, we characterize these operators using compressed shifts and finite rank operators of special kind.
It was recently proved that in some special cases asymmetric truncated Toeplitz operators can be characterized in terms of compressed shifts and rank-two operators of special form. In this paper we show that such characterizations hold in all cases.
Let $φ$ be a self-map of the unit disk and let $C_φ$ denote the composition operator acting on the standard Dirichlet space $\mathcal{D}$. A necessary condition for compactness of a difference of two bounded composition operators acting on $\mathcal{D}$, is given. As an application, a characterization of disk automorphisms $φ$ and $ψ$ for which the commutator $[C^*_ψ,C_φ]$ is compact, is given.
In 1984, a simple and useful univalence criterion for harmonic functions was given by Clunie and Sheil-Small, which is usually called the shear construction. However, the application of this theorem is limited to the planar harmonic mappings convex in the horizontal direction. In this paper, a natural generalization of the shear construction is given. More precisely, our results are obtained under the hypothesis that the image of a harmonic mapping is a sum of two sets convex in the horizontal direction.