We have just shewn how from
No A is BC,
we may obtain by conversion
No B is AC.
No C is AB,
No AB is C,
No AC is B,
No BC is A.
The proposition may also be written in the form
There is no ABC,
or, Nothing is at the same time A, B, and C.
The last of these is a specially useful form to which to bring universal negatives for the purpose of logical manipulation.
In the same way from Some A is BC or BD we may infer