STEPAKHNO, V. I. Empirical correlation operator and many-dimensional Hermite polynomials. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 6, p. 871–875, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5877. Acesso em: 5 dec. 2025.