GRAM, Christian. A remark on the construction of the centre of a circle by means of the ruler. Mathematica Scandinavica, Berkeley, CA, United States, v. 4, p. 157–160, 1956. DOI: 10.7146/math.scand.a-10466. Disponível em: https://journals.msp.org/mscand/article/view/2854. Acesso em: 25 jul. 2026.