GRIGORYAN, T.A.; LIPACHEVA, E.V.; TEPOYAN, V.H. ON $\pi$-EXTENSIONS OF THE SEMIGROUP $Z_+$. Proceedings of the YSU A: Physical and Mathematical Sciences, Yerevan, Armenia, v. 47, n. 1 (230), p. 3–5, 2013. DOI: 10.46991/PYSU:A/2013.47.1.003. Disponível em: https://journals.ysu.am/index.php/proceedings-phys-math/article/view/47_1_2013_003-005. Acesso em: 22 jul. 2024.