In mathematical logic, a literal is an atomic formula (atom) or its negation. The definition mostly appears in proof theory (of classical logic), e.g. in conjunctive normal form and the method of resolution.
Literals can be divided into two types:
For a literal
In the context of a formula in the conjunctive normal form, a literal is pure if the literal's complement does not appear in the formula.
Examples
In propositional calculus a literal is simply a propositional variable or its negation.
In predicate calculus a literal is an atomic formula or its negation, where an atomic formula is a predicate symbol applied to some terms,