Let \(\Sigma = (V_\Sigma,F_\Sigma,P_\Sigma)\) be a signature of a predicate logic. A set of predicate logic terms is defined recursively:
Take real numbers as the domain of discourse, and consider the \(\epsilon-\delta\) definition of continuous real functions:
A real function \(f:D\to\mathbb R\) is continuous at the point \(a\in D\), if for every \(\epsilon > 0\) there is a \(\delta > 0\) such that \(|f(x)-f(a)| < \epsilon\) for all \(x\in D\) with \(|x-a| < \delta.\)
This proposition can be codified using a formula like this:
\[\forall\epsilon\,(\epsilon > 0)\,\exists\delta\,(\delta > 0)\,\forall x\,(x\in D)\,(|x-a|<\delta\Longrightarrow|f(x)-f(a)|<\epsilon).\]
In this formula, the strings \("x"\), \("\delta"\), \("\epsilon"\) and \("a"\) are variables, thus they are terms. Also the constant \("0"\) as well as the functions \("f(x)"\), \("f(a)"\), \("x-a"\), \("f(x)-f(a)"\) and \("|x-a|"\), and \("|f(x)-f(a)|"\) are terms, because they are nullary, unary and binary functions.