First-order Logic
The set of terms of first-order logic (also known as first-order predicate calculus) is defined by the following rules: 1. A variable is a term. 2. If f is an n-place function symbol (with n>=0) and t_1, ..., t_n are terms, then f(t_1, ..., t_n) is a term. If P is an n-place predicate symbol (again with n>=0) and t_1, ..., t_n are terms, then P(t_1, ..., t_n) is an atomic statement.