[1] D. Duffus and I. Rival: A structure theory for ordered sets. Discrete Math. 35 (1981), 53–118. DOI 10.1016/0012-365X(81)90201-6 | MR 0620665

[2] D. Jakubíková-Studenovská: Retract irreducibility of connected monounary algebras I. Czechoslovak Math. J. 46 (121) (1996), 291–308. MR 1388617

[3] D. Jakubíková-Studenovská: Retract irreducibility of connected monounary algebras II. Czechoslovak Math. J. 47 (122) (1997), 113–126. DOI 10.1023/A:1022448406768 | MR 1435610

[4] D. Jakubíková-Studenovská: Two types of retract irreducibility of connected monounary algebras. Math. Bohem. 121 (1996), 143–150. MR 1400606

[5] D. Jakubíková-Studenovská: Retract irreducibility of monounary algebras. Czechoslovak Math. J. 49 (124) (1999), 363–390. DOI 10.1023/A:1022412604912 | MR 1692524

[6] O. Kopeček and M. Novotný: On some invariants of unary algebras. Czechoslovak Math. J. 24 (99) (1974), 219–246. MR 0347703

[7] M. Novotný: Über Abbildungen von Mengen. Pacif. J. Math. 13 (1963), 1359–1369. DOI 10.2140/pjm.1963.13.1359 | MR 0157143