G. R. IBRAHIM; S. O. MAKANJUOLA. Combinatorics Properties of Order-preserving Full Contraction Transformation Semigroup by Their Equivalence Classes. International Journal of Mathematics And its Applications, [S. l.], v. 6, n. 1 - C, p. 435–439, 2018. Disponível em: https://ijmaa.in/index.php/ijmaa/article/view/1087. Acesso em: 3 jul. 2024.