Editing Well-formed formula (section)

==Atomic and open formulas==
{{Main|Atomic formula}}

An ''atomic formula'' is a formula that contains no [[logical connective]]s nor [[Quantification (logic)|quantifiers]], or equivalently a formula that has no strict subformulas.
The precise form of atomic formulas depends on the formal system under consideration; for [[propositional logic]], for example, the atomic formulas are the [[propositional variable]]s. For [[predicate logic]], the atoms are predicate symbols together with their arguments, each argument being a [[Formation rules|term]].

According to some terminology, an ''open formula'' is formed by combining atomic formulas using only logical connectives, to the exclusion of quantifiers.<ref>Handbook of the history of logic, (Vol 5, Logic from Russell to Church), Tarski's logic by Keith Simmons, D. Gabbay and J. Woods Eds, p568 [https://books.google.com/books?id=K5dU9bEKencC&q=open+formula&pg=PA568].</ref> This is not to be confused with a formula which is not closed.