  Characterizing hybrid ASP solving in a generic way is difficult since one
needs to abstract from specific theories. Inspired by lazy SMT solving, this is
usually addressed by treating theory atoms as opaque. Unlike this, we propose a
slightly more transparent approach that includes an abstract notion of a term.
Rather than imposing a syntax on terms, we keep them abstract by stipulating
only some basic properties. With this, we further develop a semantic framework
for hybrid ASP solving and provide aggregate functions for theory variables
that adhere to different semantic principles, show that they generalize
existing aggregate semantics in ASP and how we can rely on off-the-shelf hybrid
solvers for implementation.
