CHRISTIANSEN, I. M. ’Informal activity’ in mathematics instruction. NOMAD Nordic Studies in Mathematics Education, [S. l.], v. 2, n. 3-4, p. 7–30, 1994. DOI: 10.7146/nomad.v2i3-4.146129. Disponível em: https://tidsskrift.dk/NOMAD/article/view/146129. Acesso em: 9 jan. 2025.