Formulas and ultraproducts in categories HAJNALKA ANDRÉKA; ISTVÁN NÉMETI — 1979 Beiträge zur Algebra und Geometrie = Contributions to algebra and geometry
Does 𝐒𝐏 K ⊇ 𝐏𝐒 K imply axiom of choice? Hajnal Andréka; István Németi — 1980 Commentationes Mathematicae Universitatis Carolinae
Remark on one-sided A -ideals of semigroups Hajnal Andréka; István Németi; Robert Šulka — 1983 Mathematica Slovaca