There was a mistake, but it wasn't the one you think. The derivative was incorrectly stated as N-2ap instead of N-2ap+ac. I've corrected it now. I'd apprecia

There was a mistake, but it wasn't the one you think. The derivative was incorrectly stated as N-2ap instead of N-2ap+ac. I've corrected it now. I'd appreciate another detailed check of the revised calculations.