RUMŠAS , P. The first Lithuanian book of problems in arithmetic. Psichologija, [S. l.], v. 12, p. 163–168, 1972. DOI: 10.15388/Psichol.1972.12.9274. Disponível em: https://www.zurnalai.vu.lt/psichologija/article/view/9274. Acesso em: 4 jan. 2026.