Using rearrangements of matrix-valued sequences, we prove that with certain boundary conditions the solution of the one-dimensional Schrödinger equation increases or decreases under monotone rearrangements of its potential.

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It is well known that every Hölder continuous function on the unit circle is the sum of two functions such that one of these functions extends holomorphically into the unit disc and the other extends holomorphically into the complement of the unit disc. We prove that an analogue of this holds for Hölder continuous functions on an annulus A which have zero averages on all circles contained in A which surround the hole.

Set $$\theta (s/t): = (s/t - 1)(t/s)^{\frac{{s/t}}{{s/t - 1}}} = (s - t)\frac{{t^{t/(s - t)} }}{{s^{s/(s - t)} }}$$ if 0<$t$<$s$. The key result of the paper shows that if ($T (t))$_{$t$>0}is a nontrivial strongly continuous quasinilpotent semigroup of bounded operators on a Banach space then there exists δ>0 such that ║$T(t)-T(s)$║>θ(s/t) for 0<$t$<$s$≤δ. Also if ($T(t)$)_{$t$>0}is a strongly continuous semigroup of bounded operators on a Banach space, and if there exists η>0 and a continuous function$t$→$s(t)$on [0, ν], satisfying$s$(0)=0, and such that 0<$t$<$s(t)$and ║$T(t)-T(s(t))║<θ(s/t)$for$t$∈(o, η], then the infinitesimal generator of the semigroup is bounded. Various examples show that these results are sharp.

A cooriented circle immersion into the plane can be extended to a stable map of the disk which is an immersion in a neighborhood of the boundary and with outward normal vector field along the boundary equal to the given coorienting normal vector field. We express the minimal number of fold components of such a stable map as a function of its number of cusps and of the normal degree of its boundary. We also show that this minimum is attained for any cooriented circle immersion of normal degree not equal to one.