Definition:Classes of WFFs/Sentence

Definition
Let $\mathcal L_1$ be the formal language of predicate calculus. A WFF is said to be a sentence iff it contains no free variables.

To denote particular classes of sentences, $SENT \left({\mathcal P, \mathcal F, \mathcal K}\right)$ and analogues may be used, similar to the notation for classes of WFFs.