On approximation of solutions of periodic boundary-value problems via the least square method in the critical case. Neliniini Kolyvannya, [S. l.], v. 14, n. 3, p. 419–433, 2011. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/618. Acesso em: 21 jan. 2026.