E. V. Bozhonok, “On solutions to ‘almost everywhere’ - Euler-Lagrange equation in Sobolev space $W_2^1$”, MFAT, vol. 13, no. 3, pp. 262–266, Sep. 2007, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/353