Seamus , I understand your point.
Genie ,the point I made about the double negative and mathematics was made in Chamber's History of the English Language which I don't have to hand.

Hope this isn't too much of a transgression , but seeing that so many grammar experts seem to be honing in on this thread ,here's something that has been puzzling me ......

The word "amn't" meaning "am not" is never seen written in English other than when it's being said by an Irish person in reported speech . " Well no ,I amn't going to the shop today Mr Murphy" ,for instance. But in England amn't is used widely in everyday speech pronounced as "armpt" and sometimes confused with "aren't " . A cockney might say for instance "I am supposed to be at work today , amn't I ?" But if you spell it like that ,it always reads like it's being said by an Irish person. How should amn't be spelt in English English ?