PORTENKO, N. I. On integro-differential equations for distribution of probabilities of additive functionals of diffusion processes . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 5, p. 60–68, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8441. Acesso em: 6 dec. 2025.