EBENFELT, P.; KHAVINSON, D.; SHAPIRO, H. A free boundary problem related to single-layer potentials. Annales Fennici Mathematici, [S. l.], v. 27, n. 1, p. 21–46, 2002. Disponível em: https://afm.journal.fi/article/view/135023. Acesso em: 19 may. 2024.