PEETRE, J. The Euler derivative. An intrinsic approach to the calculus of variations. MATHEMATICA SCANDINAVICA, [S. l.], v. 42, p. 313–333, 1978. DOI: 10.7146/math.scand.a-11756. Disponível em: https://www.mscand.dk/article/view/11756. Acesso em: 24 nov. 2024.