 If \(e\) is a non-empty subset of the domain \(d\), then define a variable-assignment \(s\) to be an \(e\)-assignment if for all variables \(u, s(u)\) is in \(e\). That is, \(s\) is an \(e\)-assignment if \(s\) assigns an element of \(e\) to each variable. Define \(sk(e)\), the Skolem-hull of \(e\), to be the set: