[3] Novák V.:
On the lexicographic product of ordered sets. Czechosl. Math. J. 15 (90) (1965), 270-282.
MR 0175817
[4] Sekanina M.:
On a pover of ordered sets. Archivum Math. 1 (1965), 75-82.
MR 0207600
[5] Szász G.:
Einführung in die Verbandstheorie. Teubner, Leipzig 1962.
MR 0138567