ZELENT, D. On Traczyk’s BCK-sequences. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 21, p. 43–49, 2022. Disponível em: https://studmath.uken.krakow.pl/article/view/9499. Acesso em: 4 may. 2024.