GRAM, Christian. A remark on the construction of the centre of a circle by means of the ruler. MATHEMATICA SCANDINAVICA, [S. l.], v. 4, p. 157–160, 1956. DOI: 10.7146/math.scand.a-10466. Disponível em: https://tidsskrift.dk/math/article/view/10466. Acesso em: 14 aug. 2026.