marshall wrote:
The axiom of choice is equivalent to the well-ordering principle if ZF and the rules of first-order logical induction are true.
No, that's not what I'm saying. I am not saying that the axiom of choice is true or false. I am not saying that the well-ordering principle is true or false. I am not saying that the axioms of ZF are true or false. I am not saying that the laws of first-order induction are valid or invalid.
What I am saying is that the statement "In ZF, the axiom of choice is equivalent to the well-ordering principle" is true. Translated, this means that I am saying that
there exists a proof with the following properties:
(1.) Every line is either an axiom of ZF or is deduced from the previous lines in accordance with the rules of first-order induction.
(2.) The last line says "the axiom of choice is equivalent to the well-ordering principle".
This really is true. If you don't believe it, then you can write the proof, which is a way to show that the proof exists.