LEHTO, Olli. On an extension of the concept of deficiency in the theory of meromorphic functions. Mathematica Scandinavica, Berkeley, CA, United States, v. 1, p. 207–212, 1953. DOI: 10.7146/math.scand.a-10378. Disponível em: https://journals.msp.org/mscand/article/view/2949. Acesso em: 25 jul. 2026.