[1] Graph Theory and Related Topics. (J. A. Bondy, U. S. R. Murty, eds.), Proceedings of the Conference Held in Honour of Professor W. T. Tutte on the Occasion of his Sixtieth Birthday, University of Waterloo, July 5-9, 1977, Academic Press, New York-San Francisco-London, 1979. MR 0538028

[2] GRÄTZER G.: Universal Algebra. (2nd ed.), Springer-Verlag, New York, 1979. MR 0538623

[3] JAKUBÍKOVÁ-STUDENOVSKÁ D.: Monounary algebras and bottleneck algebras. Algebra Universalis 40 (1998), 59-72. MR 1643217 | Zbl 0935.08003

[4] KISS E. W.-PÖSCHEL R.-PRÖHLE P.: Subvarieties of varieties generated by graph algebras. Acta Sci. Math. (Szeged) 54 (1990), 57-75. MR 1073419 | Zbl 0713.08006

[5] MALTSEV A. I.: Algebraic Systems. Nauka, Moscow, 1970. (Russian) MR 0282908

[6] NELSON E.: Homomorphisms of monounary algebras. Pacif. J. Math. 82 (1999), 427-429. MR 0658072

[7] NOVOTNÝ M.: Mono-unary algebras in the work of Czechoslovak mathematicians. Arch. Math. (Brno) 26 (1990), 155-164. MR 1188275 | Zbl 0741.08001

[8] NOVOTNÝ M.: Homomorphisms and strong homomorphisms of relational structures. Arch. Math. (Brno) 33 (1997), 57-64. MR 1464301 | Zbl 0909.08001

[9] NOVOTNÝ M.: Homomorphisms of heterogeneous algebras. Czechoslovak Math. J. 52 (2002), 415-428. MR 1905448 | Zbl 1016.08005

[10] OATES MACDONALD S.-VAUGHAN-LEE M.: Varieties that make one Cross. J. Aust. Math. Soc. Ser. A 26 (1978), 368-382. MR 0515754 | Zbl 0393.17001

[11] OATES-WILLIAMS S.: On the variety generated by Murskii's algebra. Algebra Univеrsalis 18 (1984), 175-177. MR 0743465 | Zbl 0542.08004

[12] PÖSCHEL R.: Shallon algebras and varieties for graphs and relational systems. In: Algеbra und Graphentheorie, Jahrestagung Algebra und Grenzgebiete 28.10.-1.11.1985 in Siebenlehn (J. Machner, G. Schaar, eds.), Bergakademie Freiberg, Sekt. Math., Siebenlehn (GDR), 1986, pp. 53-56.

[13] PÖSCHEL R.: Graph algebras and graph varieties. Algebra Universalis 27 (1990), 559-577. MR 1387902 | Zbl 0725.08002

[14] SHALLON, C R.: Nonfinitely Based Finite Algebras Derived from Lattices. Ph.D. Dissertation, U.CL.A, 1979.