Lakhan Singh, and Shailendra Kumar Gautam. “Invariant Submanifold of $\left(4k, 2k\right)$ Structure Manifold”. International Journal of Mathematics And Its Applications, vol. 4, no. 2 - C, June 2016, pp. 105-9, https://ijmaa.in/index.php/ijmaa/article/view/1051.