1. Jakubík J.: Formations of lattice ordered groups and GMV-algebras. Math. Slovaca 58, 521–534 (2008)
2. Jakubíková-Studenovská D.: On completions of partial monounary algebras. Czechoslovak Math. J. 38(113), 256–268 (1988)
3. Jakubíková-Studenovská D., Pócs J.: Monounary Algebras. Pavol Jozef Šafárik University, Košice (2009)
4. Lihová J., Pócs J.: On formations of lattices. Acta Univ. M. Belii Ser. Math. 15, 63–72 (2009)
5. Marica J.G., Bryant S.J.: Unary algebras. Pacific J. Math. 10, 1347–1359 (1960)