Not at levels A-D, which are the ones where the faults "should not be there" (citing the parent comment). At level E you only have to prove that there's no eff

Not at levels A-D, which are the ones where the faults "should not be there" (citing the parent comment). At level E you only have to prove that there's no effects of faults on safety-critical systems, so it's more about the surrounding architecture than the software itself.