Variation formulas for solution of delay differential equations taking into account mixed initial condition and delay perturbation . Neliniini Kolyvannya, [S. l.], v. 17, n. 4, p. 503–532, 2014. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/760. Acesso em: 21 jan. 2026.