(also called inference rules) or a set of axioms, or have both. A formal system is used to derive one expression from one or more other expressions. Interpretations An interpretation of a formal system is the assignment of meanings to the symbols, and truth values to the sentences of a formal system. The study of interpretations is called formal semantics. Giving an interpretation is synonymous with ''constructing a model. See also Axiomatic system Formal verification Mathematical proof Proof assistant Proof calculus Proof theory Proof (truth) De Bruijn factor References External links 2πix.com: Logic Part of a series of articles covering mathematics and logic. Archive of Formal Proofs Mizar Home Page Formal languages Proof theory Formal systems Syntax (logic) Logical truth de:Axiomatischer Beweis