## An operator without invariant subspaces on a nuclear Fréchet space.(English)Zbl 0553.47002

The author constructed an infinite dimensional nuclear Fréchet space F (which is also a nuclear countably Hilbert space, in the sense of Gelfand and Vilenkin), a backward shift T on f, $$(Tc)_ j=c_{j+1}$$, $$j=0,1,..$$. and proved that T has no invariant subspaces, but $$T^ 2$$ has an invariant subspace (theorem 2.9). The method he used to obtain the assertion is the following. He showed that the dual space of F can be identified with a certain topological algebra E, of analytic functions with varying domains and Theorem 2.9 is equivalent to that E has no closed nontrivial ideals (Theorem 3.7), then he proved Theorem 3.7.
Reviewer: Lu Shijie

### MSC:

 47A15 Invariant subspaces of linear operators 46A13 Spaces defined by inductive or projective limits (LB, LF, etc.) 46A11 Spaces determined by compactness or summability properties (nuclear spaces, Schwartz spaces, Montel spaces, etc.) 46H10 Ideals and subalgebras 46A04 Locally convex Fréchet spaces and (DF)-spaces
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