Haider ع. أ. “Geometrical Invariant element’s in Theory 2F- Mapping Between Riemannian Spaces A\(_n\) Which Have Tensors (F)\(^3\)=0”. University of Aden Journal of Natural and Applied Sciences, vol. 21, no. 2, Aug. 2017, pp. 267-7, doi:10.47372/uajnas.2017.n2.a06.