Meera Meghpara, H. M. Karavadiya, and V. J. Kaneria. “A Study on $\alpha-$graceful Labeling of Spade Graph”. International Journal of Mathematics And Its Applications, vol. 9, no. 1, Mar. 2021, pp. 113-7, http://ijmaa.in/index.php/ijmaa/article/view/108.