[1] GRÄTZER G.: Universal Algebra. The University Series in Higher Mathematics, D. Van Nostrand Company, Inc, Princeton, N.J.-Toronto-London-Melbourne, 1968. MR 0248066

[2] HALUŠKOVÁ E.: On iterated direct limits of a monounary algebra. In: Contributions to General Algebra, 10 (Klagenfurt, 1997), Heyn, Klagenfurt, 1998, pp. 189-195. MR 1648786

[3] HALUŠKOVÁ E.: Direct limits of monounary algebras. Czechoslovak Math. J, 49(124) (1999), 645-656. MR 1708334 | Zbl 1004.08003

[4] HALUŠKOVÁ E.: Monounary algebras with two direct limits. Math. Bohem. 125 (2000), 485-495. MR 1802297 | Zbl 0966.08005

[5] HALUŠKOVÁ E., PLOŠČICA M.: On direct limits of finite algebras. In: Contributions to General Algebra, 11 (Olomouc, 1998; Velke Karlovice 1998), Heyn, Klagenfurt, 1999, pp. 101-104. MR 1696661

[6] JAKUBÍK J., PRINGEROVÁ G.: Direct limits of cyclically ordered groups. Czechoslovak Math. J. 44 (1994), 231-250. MR 1281020 | Zbl 0821.06015

[7] JAKUBÍKOVÁ-STUDENOVSKÁ D.: Retract irreducibility of connected monounary algebras 1. Czechoslovak Math. J. 46 (1996), 291-307. MR 1388617

[8] JAKUBÍKOVÁ-STUDENOVSKÁ D.: Two types of retract irreducibility of connected monounary algebras. Math. Bоhem. 121 (1996), 143-150. MR 1400606 | Zbl 0863.08007

[9] JÓNSSON B.: Topics in Universal Algebra. Lecture Notes in Math. 250, Springer Verlag, Berlin, 1972. MR 0345895 | Zbl 0225.08001

[10] NOVOTNÝ M.: Über Abbildungen von Mengen. Pacific J. Math. 13 (1963), 1359-1369. MR 0157143