9.12 The logical negation operator
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The result of the logical negation operator (written ! and pronounced
'not', used in the comparison operations 'if/IF', 'for/FOR' and
'while/WHILE', is the logical negation of its operand. This means that if a
condition is TRUE, then !condition is FALSE and vice-versa.
Expressions
The expressions
IF ( NOTCARRYFLAG )... and IF (! CARRYFLAG )...
IF ( proc() == 0 )... and IF (! proc() )...
Could this be 'are equivalent'.