Better ref for P168 (cid)

[prabau]

Better reference for P168 (cid) as suggested in #1837 (comment).

[prabau]

@StevenClontz @Moniker1998 I would also like to remove the alias $\omega$C with the same PR.

Ok with you?

[Moniker1998]

@prabau why do you want to remove that alias?

[prabau]

@Moniker1998 $\omega$C was an entirely made up name for pi-base, to indicate the property that countable sets are closed. Introduced in #407.

Later we learned about the "cid" property and since that does appear in the literature and the two are equivalent, we changed the main name to "Countable sets are discrete" with "cid" as alias. Done in #890.

The omega-C had been kept as an alias, but since it was completely made up, there does not seem to be much point in keeping it.

[Moniker1998]

@prabau yeah then delete it please

[StevenClontz]

@StevenClontz @Moniker1998 I would also like to remove the alias $\omega$C with the same PR.

Ok with you?

👍