[2] Davey B.: 
Duality Theory on Ten Dollars a Day. Algebra and Orders, NATO ASI series, Vol. 389, Kluwer Acad. Publ., 1993, pp. 71–111. 
MR 1233789 | 
Zbl 0793.08001[4] Haviar M.: Extension of Birkhoff’s duality to the class of all partially ordered sets. The lecture at Conference on Univ. Alg. and Lattice Theory, Szeged (Hungary) July 1996.
[5] Mel’nik I.I.: 
Nilpotent shifts of varieties. Math. Notes 14 (1973), 692–696. 
MR 0366782[6] Ploščica M., Haviar M.: Extensions of Birkhoff’s duality to the class of all partially ordered set. Preprint 1997, 7pp.