FOLNER, Erling. Some special $W$-almost periodic sets on the integers. Mathematica Scandinavica, Berkeley, CA, United States, v. 53, p. 185–192, 1983. DOI: 10.7146/math.scand.a-12025. Disponível em: https://journals.msp.org/mscand/article/view/1643. Acesso em: 25 jul. 2026.