 The language is built on a set of of individual variables (denoted by \(x, y, z, x_1, x_2, \ldots\)), a set of function symbols (denoted by \(f, g, h, f_1, \ldots\)) where an arity is associated with each symbol (nullary function symbols are also called individual constants), and a set of predicate letters (denoted by \( R, P_1, \ldots\)) where an arity is associated with each symbol. The language contains two kinds of syntactical objects, namely terms and formulas. The terms are defined inductively as follows: