# Disjunctive normal form

2010 Mathematics Subject Classification: *Primary:* 03B05 [MSN][ZBL]

A propositional formula is said to be in *disjunctive normal form* if it is of the form
\begin{equation}\label{eq1}
\bigvee_{i=1}^n \;\bigwedge_{j=1}^{m_i} C_{ij} ,
\end{equation}
where each $C_{ij}$ ($1,\ldots,n$; $j=1,\ldots,m_i$) is either a variable or the negation of a variable. The form \ref{eq1} is realizable (is a tautology) if and only if, for each $i$, $C_{i1},\ldots,C_{im_i}$ do not contain both the formulas $p$ and $\neg p$, where $p$ is any variable. For any propositional formula $A$ it is possible to construct an equivalent disjunctive normal form $B$ containing the same variables as $A$. Such a formula $B$ is then said to be *the disjunctive normal form* of the formula $A$.

#### Comments

The dual of a disjunctive normal form is a conjunctive normal form. Both are also used in the theory of Boolean functions (cf. Boolean functions, normal forms of).

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Disjunctive normal form.

*Encyclopedia of Mathematics.*URL: http://www.encyclopediaofmath.org/index.php?title=Disjunctive_normal_form&oldid=35079