[1] A. D. BOL'BOT:
O mnogoobrazijach $\Omega $ -algebr. Algebra i logika 9, No 4 (1970), 406-414.
MR 0286733
[2] J. JEŽEK:
Principal dual ideals in lattices of primitive classes. Comment. Math. Univ. Carolinae 9 (1968), 533-545.
MR 0244131
[3] J. JEŽEK:
On atoms in lattices of primitive classes. Comment. Math. Univ. Carolinae 11 (1970), 515-532.
MR 0269571