Coherent De Morgan algebras (Q1102309)

The variety of De Morgan algebras is generated by three simple algebras: \(M_ 2\)- the two-element Boolean algebra, \(M_ 3\)- the three-element chain, and \(M_ 4\)- the four-element Boolean lattice with two fixed points under involution. The author shows that these three algebras and \(C_ 4\)- the four-element chain with no fixed points under involution, give the full list of coherent De Morgan algebras, i.e. the algebras with the property: if any subalgebra of the algebra contains a class of some congruence then that subalgebra is a union of classes of that congruence.