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[5] D. A. Romano, Some relations and subsets of semigroup with apartness generated by the principal consistent subset, Univ. Beograd. Publ. Elektroteh. Fak. Ser. Mat. 13 (2002), 7-25.

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[7] D. A. Romano, A note on quasi-antiorder in semigroup, Novi Sad J. Math. 37(1) (2007), 3-8.

[8] D. A. Romano, On regular anticongruence in anti-ordered semigroups, Publ. Inst. Math. (Beograd) (N.S.) 81(95) (2007), 95-102.

[9] D. A. Romano, The second isomorphism theorem on ordered set under antiorders, Kragujevac J. Math. 30 (2007), 235-242.

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[12] D. A. Romano, On quasi-antiorder relation on semigroup (to appear).

[13] A. S. Troelstra and D. van Dalen, Constructivism in Mathematics. An Introduction, Volume II, North-Holland, Amsterdam, 1988.