Not (')
Details
The Not operator inverts the truth value of the boolean operand. If the operand is TRUE (1), Not gives it a value of FALSE (0). If the operand is FALSE (0), Not gives it a value of TRUE (1).
Examples
For example, the following statements produce a result of FALSE (0):
SET x=0
WRITE x
While the following statements produces a result of TRUE (1).
SET x=0
WRITE 'x
The Not operator combined with a comparison operator inverts the sense of the comparison. For example, the following statement displays a result of FALSE (0):
WRITE 3>5
But, the following statement displays a result of TRUE (1):
WRITE 3'>5