User blog comment:Deedlit11/Ordinal Notations III: Collapsing Higher Cardinalities/@comment-7484840-20130706154845/@comment-7484840-20130706182122

I know in the psi function, $$\psi_2(\Omega_3) = \alpha\mapsto\psi_2(\alpha)$$, and then  $$\psi_2(0) = \alpha\mapsto\Omega_2^{\alpha} $$, and I though that the theta function was very similar.