Say A is empty.
Could I do A --> B (1-1) or B --> A (1-1)?
Thanks.
Every mapping is injective. To see this merely note that for the condition that there exists such that we would have to say . See a problem?
For it actually reverts to the same thing. For suppose that then for any we would have that does not exist? Why? Thus, if and is well-defined then by necessity we must have that .