Conjunctive normal form with example
The steps to convert to conjunctive normal form:
1. Eliminate by using the fact that a  b is equivalent to ~a V b
2. Reduce the scope of negation:
~(A V B) = ~A B ~(A  B) = ~A V B
De Morgan's law: ~x P(x) = x ~P(x)
~x P(x) = x ~P(x)
3. Standardize variables so that each quantifier binds a unique variable.
x P(x) V x Q(x) would be converted to
x P(x) V y Q(y)
4. Move all quantifiers to the left of the formula without changing their
relative order.
x y P(x) V Q(y)
5. Eliminate existential quantifiers. A formula that contains an
existentially quantified variable asserts that there is a value that can
be substituted for the variable that makes the formula true.
y President(y) can be transformed into President(S1)
If existential quantifiers occur within the scope of a universal quantifier
then the value that satisfies the predicate may depend on the values of
the universally quantified variables.
x y father_of(y, x) can be transformed into x father_of(S2(x), x)
These generated functions are called Skolem functions.
6. Drop the prefix.
7. Convert the matrix into conjunction of disjuncts.
8. Call each conjunct a separate clause