On a question of Pultr regarding categories of structures James S. Williams (1974) Commentationes Mathematicae Universitatis Carolinae
On relational selections for complete theories. Klaus Kaiser (1978) Archiv für mathematische Logik und Grundlagenforschung
On some properties a projective model class passes on to the generated axiomatic class. Klaus Kaiser, M. Armbrust (1974) Archiv für mathematische Logik und Grundlagenforschung
On the congruence lattice of stable algebras with definability of compact congruences Sauro Tulipani (1983) Czechoslovak Mathematical Journal