A characterization of quasivarieties of partial algebras by means of limits and products.
A note on cylindric lattices
0. Introduction. Besides being of intrinsic interest, cylindric (semi-) lattices arise naturally from the study of dependencies in relational databases; the polynomials on a cylindric semilattice are closely related to the queries obtainable from project-join mappings on a relational database (cf. [D] for references). This note is intended to initiate the study of these structures, and only a few, rather basic results will be given. Some problems at the end will hopefully stimulate further research....
A note on idempotent modifications of groups
The idempotent modification of a group is always a subdirectly irreducible algebra.