KAC, I. S.; PIVOVARCHIK, V. N. On Barcilon’s formula for Krein’s string. Methods of Functional Analysis and Topology, [S. l.], v. 23, n. 3, p. 270–276, 2017. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/670. Acesso em: 15 dec. 2025.