MERKYS, V. Über die Reduzierbarkeit eines zweidimensionalen Systems von Differentialgleichungen. Lithuanian Mathematical Journal, [S. l.], v. 9, n. 4, p. 755–760, 1969. DOI: 10.15388/LMJ.1969.20817. Disponível em: https://www.journals.vu.lt/LMJ/article/view/20817.. Acesso em: 2 may. 2024.