jsfisher
ETcorngods survivor
- Joined
- Dec 23, 2005
- Messages
- 24,532
EDIT:
Consider A={1,2} and B={X,Y,Z}
f1(1) = X
f1(2) = Y
that is also can be written as
Code:{1,2} ↓ ↓ {X,Y,Z}
So, there is one case of no function from all the elements of A to some element of B (element Z, in this case), and we can conclude that |A|<|B|.
No. That does not follow the very definition you provided. This is a case where we have a doron-function which maps every element of A to some element of B. There was a doron-mapping for 1 and a doron-mapping for 2; all the elements of A have a doron-mapping.
Therefore, |A| = |B|. That's according to your doron-cardinality definition.
By the way, "there is one case of no function" is gibberish. You cannot have "one case" of "no function". Cases show examples of things, not the lack of any possible example. Saying "no function" would mean there is no possible example that meets whatever criterion is under consideration.