KHALINA, K. S. Boundary controllability problems for the equation of oscillation of an inhomogeneous string on a semiaxis. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 4, p. 525–541, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2593. Acesso em: 14 apr. 2025.