Special elements in lattices of semigroup varieties

Abstract

We survey results concerning special elements of nine types (modular, lower-modular, upper-modular, cancellable, distributive, codistributive, standard, costandard and neutral elements) in the lattice of all semigroup varieties and certain its sublattices, mainly in the lattices of all commutative varieties and of all overcommutative ones. Several open questions are formulated. The work is regularly updated and modified as new results and/or articles appear.