@article{PIM_1989_N_S_46_60_a21,
     author = {Adnan Al-Aqeel},
     title = {On {Riemannian} 4-symmetric {Manifolds}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {163 },
     year = {1989},
     volume = {_N_S_46},
     number = {60},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1989_N_S_46_60_a21/}
}