Papanicolaou, N., and C. I. Christov. “GALERKIN SPECTRAL METHOD FOR HIGHER-ORDER BOUNDARY VALUE PROBLEMS ARISING IN THERMAL CONVECTION”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 94, Dec. 2002, pp. 71-83, https://annual.uni-sofia.bg/index.php/fmi/article/view/191.