@article{ARM_1999__35_2_a3,
     author = {Alexieva, Yana and Ivanov, Stefan},
     title = {Riemannian manifolds in which certain curvature operator has constant eigenvalues along each helix},
     journal = {Archivum mathematicum},
     pages = {129--140},
     publisher = {mathdoc},
     volume = {35},
     number = {2},
     year = {1999},
     mrnumber = {1711665},
     zbl = {1054.53058},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ARM_1999__35_2_a3/}
}