Dhaliwal, R.S., et al. “On Closed-Form Solutions of Triple Series Equations Involving Laguerre Polynomials”. Ukrains’kyi Matematychnyi Zhurnal, vol. 62, no. 2, Feb. 2010, pp. 231 – 237, https://umj.imath.kiev.ua/index.php/umj/article/view/2859.