PIVOVARCHIK, V. N. Inverse problem for a string with concentrated mass at one end. Methods of Functional Analysis and Topology, [S. l.], v. 4, n. 3, p. 61–71, 1998. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/69. Acesso em: 18 dec. 2025.