 Let \(K\) be a set of non-logical terminology. An interpretation for the language \(\LKe\) is a structure \(M = \langle d,I\rangle\), where \(d\) is a non-empty set, called the domain-of-discourse, or simply the domain, of the interpretation, and \(I\) is an interpretation function. Informally, the domain is what we interpret the language \(\LKe\) to be about. It is what the variables range over. The interpretation function assigns appropriate extensions to the non-logical terms. In particular,