Definition:Classes of WFFs/Plain Sentence
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Definition
Let $\LL_1$ be the language of predicate logic.
A WFF is said to be a plain sentence if and only if it is both plain and a sentence.
That is, if and only if it contains free variables nor parameters.
Thus, plain sentences are those WFFs which are in $\map {SENT} {\PP, \FF, \O}$.
Sources
- 1996: H. Jerome Keisler and Joel Robbin: Mathematical Logic and Computability: $\S 2.3$