Positive Operators and Plus-operators in Krein Spaces
Positive operators in a Krein space (Sections 1 and 3) have turned out (see Chapter VIII, especially Section 6 and the Notes) to be the most fruitful generalizations of positive operators in Hilbert space. In Section 2 an alternative extension of the latter concept is considered. Sections 4–6 resume the study of plus-operators begun in Section II.8. A unifying feature of the chapter is the repeated application of the Schwarz inequality. Theorems 1.3, 3.1, 5.2, 5.4, 5.5 and 6.1 deserve particular attention.
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