[Gerald C Koch]

The makers of 135mm enlarging lenses for 4x5 film have not heard of your rule.

Perhaps I should have said rule of thumb. The same rule applies to taking lenses. Yes you're right but you have to be careful in making a choice. As with most things in photography there are tradeoffs. There are 135 mm lens which will cover a 4x5 negative but they contain more elements and are more expensive. The cheaper ones may cause distortion, lower contrast, or light dropoff at the corners of the print.