Apple iWork '09 - Manual (Page 164)

NOT
The NOT function returns the opposite of the Boolean value of a specified expression.
NOT(any-expression)
 any-expression: An expression to be tested. any-expression can contain anything as
long as the expression can be evaluated as a Boolean. If the expression evaluates to
a number, 0 is considered to be FALSE, and any other number is considered to be
TRUE.
Examples
=NOT(0) returns TRUE because 0 is interpreted as FALSE.
=OR(A9, NOT(A9)) always returns TRUE because either A9 or its opposite will always be true.
=NOT(OR(FALSE, FALSE)) returns TRUE because neither argument of the logical OR is true.
Related Topics
For related functions and additional information, see:
“AND” on page 156
“IF” on page 158
“OR” on page 165
“Listing of Logical and Information Functions” on page 155
“Value Types” on page 36
“The Elements of Formulas” on page 15
“Using the Keyboard and Mouse to Create and Edit Formulas” on page 26
“Pasting from Examples in Help” on page 41
164 Chapter 7 Logical and Information Functions