I may as well give Doron one more thing to wake up to.
Consider just this one conditional:
If there is a doron-function from A to B such that for each a in A there is at most one b in B AND for each b in B there is exactly one a in A AND there is at least one a in A that does not have any b in B then |A| > |B|.
The antecedent has three requirements for a doron-function from A to B:
- for each a in A there is at most one b in B
- for each b in B there is exactly one a in A
- there is at least one a in A that does not have any b in B
The first of the three is redundant with the basic definition of a doron-function. For any doron-function from X to Y, every element of X corresponds to either zero or one element of Y. So, we can discard the explicit statement of this requirement.
The second requirement states that every element in the range (aka codomain) is the image of exactly one element in the doron-function's domain. That's a slightly stronger condition than "onto"; more importantly, it means the inverse of the doron-function is an injection, a one-to-one function (and a real function, too, not a doron-function).
We can restate the conditional, then, thusly:
If there is a function from B to A such that the function is an injection and there is at least one a in A that is not the image of any element of B then |A| > |B|.
Or, more simply:
If there is an injection from B to A that is not surjective then |A| > |B|.
A couple things to note: First, a redefinition of what was meant by function was totally unnecessary. Doron tends to work through things backwards, and the redefinition was a outgrowth of that, but it was unnecessary (as was mentioned a few times).
Second, this version of the conditional is very similar to the real definition. It is a straight conditional instead of a biconditional, and it prohibits surjection, but the former came about because of Doron's misconception of biconditionals (I'd steered him towards framing his definitions in that form, but he later rebelled), and the latter is a more a matter of Doron trying to force <, =, and > as explicit results rather than produce a consistent result. With surjection permitted, the result becomes |A| >= |B|.
It is the surjection prohibition that makes doron-cardinality misbehave for non-finite sets.