lo.logic - What is induction up to epsilon_0?

This is a question asked out of curiosity, and because I can't understand the wikipedia page.

I have often been told that PA cannot prove the validity of induction up to $epsilon_0$, which has been expressed to me roughly as the claim that $epsilon_0$ is well-ordered. I understand what ordinals are, and what $epsilon_0$ is. I also understand first order logic and axiom schemes, so I understand how the induction axiom scheme formalizes the notion that $omega$ is well-ordered.

What I don't understand is how one could formulate the statement that $epsilon_0$ is well-ordered as a first order sentence in arithmetic. Would someone mind spelling this out for me?

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