V. D. Derech, “Characterization of the semilattice of idempotents of a finite-rank permutable inverse semigroup with zero”, Ukr. Mat. Zhurn., vol. 59, no. 10, pp. 1353–1362, Oct. 2007, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3394