Totally geodesic hypersurfaces of naturally reductive homogeneous spaces (Q1356391)

B.-Y. Chen and T. Nagano proved that a simply connected, irreducible symmetric space has constant sectional curvature if and only if it admits a totally geodesic hypersurface. K. Tojo extended this result to the class of simply connected irreducible naturally reductive spaces of dimension 3, 4 and 5 and to that of the normal homogeneous spaces. In this paper, the author proves that the result still holds when the restriction on the dimension is deleted.