I've always been interested in having a good understanding of Gentzen's proof of the consistency of arithmetic.

Being more precise, he showed that $PRA + WF(\epsilon_0) \vdash Con(PA)$.

I am interested in an exposition of his work that

**1)** Is transparent on which parts of the consistency proof uses the well-foundness of $\epsilon_0$.

**2)** Discuss (in mathematical and philosphical way) to what extent this proof deviate from the original Hilbert's Program, and in what extent it fits in a nice way to a more flexible formulation of this programme.

I should also add:

**0)** Is technically as simple as possible.

Item **0)** is because I think this question might be of interest to the curious general mathematician.