Abstract
Contractive linear relations in Hilbert spaces are (graphs of) operators, but in spaces with an indefinite metric this is not always true. The presence of a multivalued part gives difficulties in the characterization of maximal contractive linear relations and in the proof of the existence of invariant subspaces. These topics are considered in this note.
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Azizov, T.Y., Dijksma, A. (1998). Contractive linear relations in Pontryagin spaces. In: Gohberg, I., Mennicken, R., Tretter, C. (eds) Recent Progress in Operator Theory. Operator Theory Advances and Applications, vol 103. Birkhäuser, Basel. https://doi.org/10.1007/978-3-0348-8793-9_2
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