KRÍZEK, Michal; NEITTAANMÄKI, Pekka. On the validity of Friedrichs’ inequalities. Mathematica Scandinavica, Berkeley, CA, United States, v. 54, p. 17–26, 1984. DOI: 10.7146/math.scand.a-12037. Disponível em: https://journals.msp.org/mscand/article/view/1590. Acesso em: 25 jul. 2026.