1. On the structure of abstract algebras;Birkhoff;Proc. Cambridge Philos. Soc.,1935
2. Possible cardinalities of irredundant bases for finite closure structures;Givant;Discrete Math.,1975
3. Equational spectra and reduction of identities;Grätzer;Notices Amer. Math. Soc.,1967
4. Symmetric difference in abelian groups;Grätzer;Pacific J. Math.,1978
5. The minimum cardinality of equational bases for varieties of groups and rings;Green;Notices Amer. Math. Soc.,1970