CUPPINGS AND CAPPINGS IN ENUMERATION (delta)2 -DEGREES

We deal with a semilattice of (delta)-degrees, i.e., degrees that contain some set from a class (delta) of the arithmetic hierarchy. It is proved that there exists an incomplete (pi)1-degree which lacks cappings in enumeration (delta)2-degrees. On the other hand, it turns out that every low e-degree does have a capping in (delta)2-e-degrees.