Large Veblen ordinal

In set theory, the large Veblen ordinal is a certain kind of large countable ordinal number, named after Oswald Veblen.

There is no standard notation for ordinals beyond the Feferman–Schütte ordinal $\Gamma _{0}$. Most systems of notation use symbols such as $\psi (\alpha )$, $\theta (\alpha )$, or $\psi _{\alpha }(\beta )$, some of which are modifications of the Veblen functions to produce countable ordinals even for uncountable arguments, and some of which are ordinal collapsing functions.

The large Veblen ordinal is sometimes denoted by $\theta (\Omega ^{\Omega })$ or $\psi (\Omega ^{\Omega ^{\Omega }})$. It was constructed by Veblen using an extension of Veblen functions allowing infinitely many arguments.

References

• Veblen, Oswald (1908). "Continuous increasing functions of finite and transfinite ordinals". Transactions of the American Mathematical Society. 9 (3): 280–292. JSTOR 1988605.

• Weaver, Nik (2009). "Predicativity beyond Γ₀". arXiv:math/0509244.