what is a cofinal sequence?

527 Views Asked by At

enter image description here

I understand that the subset $\Phi'$ of $\Phi$ is cofinal by looking at Wikipedia

https://en.wikipedia.org/wiki/Cofinal_(mathematics)

Would anybody explain what the cofinal sequence $(Y_n)$ means?

1

There are 1 best solutions below

0
On BEST ANSWER

It means that the range of the sequence ($Y_n$), i.e. {$Y_n$}, is a cofinal subset of $\Phi$.

In other words, the set {$Y_n$} is a special cofinal subset of $\Phi$: It is indexed by the natural numbers. Moreover, the subset requirements $Y_1$ $\subset$ $Y_2$ $\subset$ ... restrict how the indexes are assigned.