How much sweetness is there in the universe?

Iterating the recursively Mahlo operations

In this paper we address a problem: How far can we iterate lower recursively Mahlo operations in higher reflecting universes? Or formally: How much can lower recursively Mahlo operations be iterated in set theories for higher reflecting universes? It turns out that in $Π_N$-reflecting universes the lowest recursively Mahlo operation can be iterated along towers of $Σ_1$-exponential orderings of height $N-3$, and that all we can do is such iterations. Namely the set theory for $Π_N$-reflecting universes is proof-theoretically reducible to iterations of the operation along such a tower.