0000000000940704
AUTHOR
Johannes Ueberberg
A characterization of the line set of an odd-dimensional Baer subspace
Generalizing a theorem of Beutelspacher and Seeger, we consider line sets\(\mathcal{L}\) inP=PG(2t + 1,q),t ∈ IN, with the following properties: (1) any (t + 1)-dimensional subspace ofP contains at least one line of\(\mathcal{L}\), (2) if a pointx ofP is incident with at least two lines of\(\mathcal{L}\) then the points in the factor geometryP/x which are induced by the lines of\(\mathcal{L}\) throughx form a blocking set of type (t, 1) inP/x, (3) any line of\(\mathcal{L}\) is coplanar with at least one further line of\(\mathcal{L}\). We will show that the examples of minimal cardinality are exactly the line sets of Baer subspaces ofP.
Zur Spektralinvarianz von Algebren von Pseudodifferentialoperatoren in derL p -Theorie
Die Hormander-Klassen Ψ1,δ0 (0≤δ<1) von Pseudodifferentialoperatoren sind Ψ-Algebren. Insbesondere ist die Inverse eines inL(Lp(ℝn)) invertierbaren Pseudodifferentialoperators der Klasse Ψ1,δ0 selbst wieder ein Pseudodifferential-operator derselben Klasse.