Gol’dman, N. “Application of the Duality Principle in Inverse Problems for Parabolic Equations With Unknown Right-Hand Sides”. Numerical Methods and Programming (Vychislitel’nye Metody I Programmirovanie), vol. 15, no. 39, Mar. 2014, pp. 130-42, https://en.num-meth.ru/index.php/journal/article/view/756.