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Towards a theory of some unbounded linear operators on $$p$$-adic Hilbert spaces and applications. (English) Zbl 1087.47061
The author presents some examples of (un-)bounded operators acting on a “$$p$$-adic Hilbert space” $$E$$. This is a free Banach-space endowed with a bilinear form satisfying the Cauchy-Schwarz inequality. It should be mentioned that only little is known about such structures (cf., in particular, the references to Bertin Diarra’s papers in the article under review). The paper, therefore, is mainly dedicated to a study of particular examples.
The question of the existence of adjoints of unbounded operators is addressed; a satisfying characterization, however, is not achieved. Motivated by the established characterization of bounded operators with adjoint, the author introduces the notion of “an operator $$A$$ which is said to have an adjoint $$A^*$$ if and only if it satisfies condition (2.2)” (cf. Definition 2.2 in the paper). It is, however, not proven in the sequel that this notion is necessary for the existence of an adjoint of $$A^*$$ in the usual sense. This interesting question therefore remains open.
The paper contains the following misprints:
Proof of Proposition 2.4 (page 211, line 9): “what we have to show” is “there exists a positive integer $$i$$ such that...” (quantifiers). Proof of Theorem 5.1 (last line of the proof): the conclusion “$$A$$ has norm $$1$$, hence $$A$$ is an isometry” should be replaced by “$$A-I$$ has norm strict less than $$1$$, therefore $$A$$ is an isometry.”

MSC:
 47S10 Operator theory over fields other than $$\mathbb{R}$$, $$\mathbb{C}$$ or the quaternions; non-Archimedean operator theory 46S10 Functional analysis over fields other than $$\mathbb{R}$$ or $$\mathbb{C}$$ or the quaternions; non-Archimedean functional analysis 47A05 General (adjoints, conjugates, products, inverses, domains, ranges, etc.) 47B25 Linear symmetric and selfadjoint operators (unbounded)
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References:
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