Zadiraka К. V.; Lоs G. A. On the stability and instability of solutions of linear differential equations of the $n$th order with periodic coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 6, p. 117–122, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8467. Acesso em: 6 dec. 2025.