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On geodesic mappings of $$m$$-symmetric and generally semi-symmetric spaces. (English. Russian original) Zbl 0816.53009
Russ. Math. 36, No. 8, 38-42 (1992); translation from Izv. Vyssh. Uchebn. Zaved., Mat. 1992, No. 8(363), 42-46 (1992).
This article is devoted to strengthening and generalizing a number of results of the same author investigating the problem of non-trivial geodesic mappings (abbreviate NGM). In [Math. Publ. (Opava). 1, 151-156 (1993; Zbl 0805.53061)], Ž. Radulovič and the author established that non-flat $$V_ n$$ whose Riemann tensor satisfies (1) $$R_{hijk,\ell_ 1,\dots,\ell_ m} = R_{hi\alpha \beta} S^{\alpha \beta}$$ ($$S$$ is a tensor), do not admit NGM under the condition (2) $$a_{ij,k} = \lambda_{(i}g_{j)k}$$, $$\lambda_{ij} = \mu g_{ij}$$, $$\mu$$ is a constant, where $$g_{ij}$$ is the metric tensor, $$a_{ij}$$ is a symmetric tensor, $$\lambda_ i$$ is a non-zero vector and $$(i,j)$$ is symmetrization.
The main theorem of this paper is a generalization of a result of the article quoted above, replacing (1) by the existence of a tensor $$T_{h_ 1,\dots, h_ m}$$; $$n \geq 2m-1$$ not representable as a tensor sum of products of invariants and the metric tensor which satisfies: $\sum^ m_{s = 1} T_{h_ 1 \dots h_{s-1}} \alpha h_{s + 1} \dots h_ m(R^ \alpha_{h_ sjk} - B(\delta^ \alpha_ j g_{h_ sk} - \delta^ \alpha g_{hsj}))$ where $$\delta^ h_ j$$ are Kronecker symbols and $$B$$ is invariant. The spaces in which this condition is satisfied have been called $$T$$-generalized semi-symmetrical $$\{TP_ n(B)\}$$ and $$T$$-semi-symmetrical $$\{TP_ n(0)\}$$. It is demonstrated that an $$m$$-symmetrical $$V_ n$$ $$(n \geq 2m + 3)$$ of non- constant curvature or a Riemannian space $$V_ n$$ $$(n \geq 2m)$$ which satisfies: $$(R_{_ ij,k} - R_{ik,j})_{e_ 1,\dots,e_ m} = 0$$, $$R_{ij,k} - R_{ik,j} \neq 0$$ where $$R_{ij}$$ is the Ricci tensor, do admit either non-trivial projective transformations, or non-trivial geodesic mappings.
Reviewer: S.Noaghi (Vulcan)

##### MSC:
 53B20 Local Riemannian geometry
##### Keywords:
$$m$$-symmetric space; geodesic mappings