User blog comment:SuperSpruce/Can someone teach me how Rathjen’s OCF works?/@comment-35470197-20190723090522/@comment-36984051-20190726123127

Do I know cofinality well enough?

Cof(α) is defined as the length of the fundamental sequence of α.

Cof(0) = 0; Cof (β) = 1, where β is a successor ordinal.

Cof(γ) = ω, where γ is a countable, recursive, limit ordinal.

Cof(Ω) = Ω.