[1] BIRKHOFF G.:
On the combination of subalgebras. Proc. Cambridge Philos. Soc., 29, 1933, 441-464.
Zbl 0007.39502
[3] WHITMAN P. M.:
Lattices, equivalence relations and subgroups. Bull. Amer. Math. Soc., 52, 1946, 507-522.
MR 0016750 |
Zbl 0060.06505