KIRJACKIJ, E. G. Using variational formulae for solving extremal problems in linearly‐invariant classes. Mathematical Modelling and Analysis, [S. l.], v. 2, n. 1, p. 105–116, 1997. DOI: 10.3846/13926292.1997.9637073. Disponível em: https://journals.vilniustech.lt/index.php/MMA/article/view/10019. Acesso em: 9 may. 2025.