Marinov, T., and C. Christov. “Method of Variational Imbedding for Identification of Heat-Conduction Coefficient from Overposed Boundary Data”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 91, Dec. 1999, pp. 215-2, https://ftl5.uni-sofia.bg./index.php/fmi/article/view/280.