QUASIVARIETIES OF IDEMPOTENT SEMIGROUPS
M. E. Adams, W. Dziobiak · International Journal of Algebra and Computation · 2003
It is proved that the lattice L(Bd) of quasivarieties contained in the variety Bdof idempotent semigroups contains an isomorphic copy of the ideal lattice of a free lattice on ω free generators. This result shows that a problem of Petrich [19], which calls for a description of L(Bd), is much more complex than originally expected.