NOT _ _ _ _ _ _ _ _ _ _ _ _ operator
The not operator returns true if its argument evaluates to nil, and nil if its argument is true .
not(<logical expression>)
if not numberp(a) then write "indeterminate" else write a; indeterminate; a := 10; A := 10 if not numberp(a) then write "indeterminate" else write a; 10 if not(numberp(a) and a < 0) then write "positive number"; positive number
Logical operators can only be used in conditional statements such as
if...then...else or while...do.