AGARD, S.; FEHLMANN, R. On the extremality and unique extremality of affine mappings in space. Annales Fennici Mathematici, [S. l.], v. 11, n. 1, p. 87–110, 1986. DOI: 10.5186/aasfm.1986.1101. Disponível em: https://afm.journal.fi/article/view/134564. Acesso em: 11 apr. 2025.