# Definition:Classes of WFFs/Plain WFF

Jump to navigation
Jump to search

## Definition

A **plain WFF** of predicate logic is a WFF with no parameters.

Thus $\map {WFF} {\PP, \FF, \O}$ is the set of all **plain WFFs** with relation symbols from $\PP$ and function symbols from $\FF$.

It is immediate that a **plain WFF** is a WFF with parameters from $\KK$ for *all* choices of $\KK$.

## Sources

- 1996: H. Jerome Keisler and Joel Robbin:
*Mathematical Logic and Computability*: $\S 2.3$