Propositional formula

Definition
Propositional formula is a well-formed expression of propositional logic. What counts as a propositional formula is defined by the syntax of propositional logic:

(i) a propositional letters in the vocabulary of L are formulas in L     b  if psi is a formula of L, Neg psi is too c if phi and psi are formulas in L, (phi &amp; psi), (phi V psi), (phi -&gt; psi) and (phi &lt;-&gt; psi) are too d only that which can be generated by the clauses (a)-(c) in a        finite number of steps is a formula in L.

The clauses (a)-(c) define what counts as a formula; clause (d) states that nothing else can be a formula of L.

Links

 * Utrecht Lexicon of Linguistics