View Single Post
Feb23-12, 09:55 PM
Sci Advisor
P: 1,172
Another perspective: you can maybe rigorize it by saying:

a in B or a in C , but a not in B , so we must have a in C:

Basically, as you rightly concluded, a must be in one

of B or C, but ,by assumption/construction, a is not in B,

so a must be in C.