In [1], Jakubík showed that the class of $\sigma $-interpolation lattice-ordered groups forms a radical class, but left open the question of whether the class forms a torsion class. In this paper, we show that this class does indeed form a torsion class.
In this article, it will be shown that every $\ell $-subgroup of a Specker $\ell $-group has singular elements and that the class of $\ell $-groups that are $\ell $-subgroups of Specker $\ell $-group form a torsion class. Methods of adjoining units and bases to Specker $\ell $-groups are then studied with respect to the generalized Boolean algebra of singular elements, as is the strongly projectable hull of a Specker $\ell $-group.