;Pure literal elimination : If a propositional variable occurs with only one polarity in the formula, it is called " pure ".
12.
The precise form of atomic formulas depends on the logic under consideration; for propositional logic, for example, the atomic formulas are the propositional variables.
13.
Propositional variables should not be confused with the metavariables which appear in the typical axioms of propositional calculus; the latter effectively range over well-formed formulae.
14.
Here atoms ( ? ) is the set of propositional variables occurring in ?, and ?" is the semantic entailment relation for propositional logic ."
15.
The term " tautology " began to be applied to those propositional formulas that are true regardless of the truth or falsity of their propositional variables.
16.
Formally, propositional models can be represented by sets of propositional variables; namely, each model is represented by the set of propositional variables it assigns to true.
17.
Formally, propositional models can be represented by sets of propositional variables; namely, each model is represented by the set of propositional variables it assigns to true.
18.
For example, in a propositional formula, each propositional variable may be interpreted as a concrete proposition, so that the overall formula expresses a relationship between these propositions.
19.
Tautologies are a key concept in propositional logic, where a tautology is defined as a propositional formula that is true under any possible Boolean valuation of its propositional variables.
20.
:US . Let \ phi ( p ) be a formula with one or more instances of the propositional variable p, and let \ psi be another formula.
