[1] D. Duffus, 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] W. Imrich, S. Klavžar: Retracts of strong products of graphs. Discrete Math. 109 (1992), 147–154. DOI 10.1016/0012-365X(92)90285-N | MR 1192377

[3] D. Jakubíková: Homomorphisms of unary algebras. Math. Slovaca 26 (1976), 317–322. (Russian ) MR 0429698

[4] D. Jakubíková: Systems of unary algebras with common endomorphisms I. Czechoslovak Math. J. 29 (1979), 406–420, II. ibid., 421–429. MR 0536068

[5] S. Klavžar: Two remarks on retracts of graph products. Discrete Math. 109 (1992), 155–160. DOI 10.1016/0012-365X(92)90286-O | MR 1192378

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

[7] T. Kuczmanov, S. Reich, M.  Schmidt, A.  Stachura: The product retraction property for the $c_0$-product of countable many metric spaces. Math. Japonica 39 (1994), 73–80.

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

[9] M. Novotný: Construction of all homomorphisms of unary algebras. Dept. Math. Ped. Fac. Univ. J.  E. Purkyně, Seminar on new directions in mathematical education, Brno, 1973. (Czech)