TUTAJ, E. On a certain characterisation of the semigroup of positive natural numbers with multiplication. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 21, p. 71–92, 2022. Disponível em: https://studmath.up.krakow.pl/article/view/9607. Acesso em: 6 dec. 2023.