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4 papers · 2 filters
Pontryagin Space Structure in Reproducing Kernel Hilbert Spaces over *-semigroups
Franciszek Hugon Szafraniec, Michal Wojtylak
The geometry of spaces with indefinite inner product, known also as Krein spaces, is a basic tool for developing Operator Theory therein. In the present paper we establish a link b…
Extending positive definiteness
D. Cichoń, J. Stochel, F. H. Szafraniec
The main result of the paper gives criteria for extendibility of sesquilinear form-valued mappings defined on symmetric subsets of *-semigroups to positive definite ones. By specif…
Componentwise and Cartesian decompositions of linear relations
S. Hassi, H. S. V. de Snoo, F. H. Szafraniec
Let be a, not necessarily closed, linear relation in a Hilbert space $\sH$ with a multivalued part $\mul A$. An operator in $\sH$ with $\ran B\perp\mul A^{**}$ is said to b…
Decomposing numerical ranges along with spectral sets
F. H. Szafraniec
This note is to indicate the new sphere of applicability of the method developed by Mlak as well as by the author. Restoring those ideas is summoned by current developments concern…