Literal (Propositional Logic)

Definition

Literal (Propositional Logic)

A literal is an atom or the negation of an atom.

• A positive literal is an atom $p$ (positive literal).
• A negative literal is the negation $\neg p$ of an atom (negative literal).

Every clause and every conjunctive normal form is built from literals.

Examples

Example

$p$ and $\neg q$ are literals.

Example

$\neg \neg p$ is not a literal, because it is the negation of $\neg p$, not of an atom.