Partial Differential Equations That Are Hard to Classify. Journal of Partial Differential Equations, [S. l.], v. 25, n. 1, p. 41–65, 2012. DOI: 10.4208/jpde.v25.n1.4. Disponível em: https://gsp.tricubic.dev/jpde/article/view/4205. Acesso em: 15 mar. 2026.