Definition:Classes of WFFs

Definition
Let $\LL_1$ denote the language of predicate logic.

The set of all WFFs of $\LL_1$ formed with relation symbols from $\PP$ and function symbols from $\FF$ can be denoted $\map {WFF} {\PP, \FF}$.

If so desired, the parameters can also be emphasized by writing $\map {WFF} {\PP, \FF\ ,KK}$ instead.

To specify $\PP$, one speaks of WFFs with relation symbols from $\PP$.

To specify $\FF$, one speaks of WFFs with function symbols from $\FF$.

To specify $\KK$, one speaks of WFFs with parameters from $\KK$.

Of course, combinations of these are possible.

Several classes of WFFs are often considered and have special names.