[1] Z. HEDRLÍN A. PULTR: 
On full embeddings of categories of algebras. Illinois J. of Math., 10 (1966), 392-406. 
MR 0191858 
[3] A. PULTR: 
Eine Bemerkung über volle Einbettungen von Kategorien von Algebren. Math. Annalen, 178 (1968), 78-82. 
MR 0230794 | 
Zbl 0174.30002 
[4] J. SICHLER: 
Concerning minimal primitive classes of algebras containing any category of algebras as a full subcategory. Comment. Math. Univ. Carolinae 9 (1968), 627-635. 
MR 0252305 | 
Zbl 0204.33301 
[5] P. VOPĚNKA A. PULTR Z. HEDRLÍN: 
A rigid relation exists on any set. Comment. Math. Univ. Carolinae 6 (1965), 149-155. 
MR 0183647