I don't understand this

[Daniel]

On 2023-06-10 05:54, Tom Goldring wrote:
> To get the symbol "aleph null" typically used to denote the cardinality 
> of the set of natural numbers, I can simply type the eight keystrokes 
> \aleph_0 and it will show up in LyX correctly.
> 
> Now suppose I want the set whose members are all countable subsets of 
> the real numbers. This is typically denoted as R_\aleph_0 (where by "R" 
> I don't mean the ordinary letter capital R, I mean the symbol 
> $\mathbb{R}$ that is used to denote the set of real numbers, which I can 
> get in math mode from the "del" (inverted triangle) menu. In other 
> words, it's "R" with subscript "aleph null".
> 
> Here's the part I don't understand. If I put in the "R" followed by 
> _\aleph_0, the R and the aleph show up correctly, but the zero (the 
> subscript of the aleph) shows up as a different character (I think it's 
> the character that's used in formal logic to mean something like "is not 
> a proof of").
> 
> Could someone please explain to me what is going on here? I can't make 
> any sense out of it.

I do not know why it is showing different symbols. But the solution is 
to enter the \aleph_0 *outside* of the \mathbb. This is not LyX specific 
but the case in LaTeX in general. Do do so in LyX you need to first step 
out of the \mathbb inset (indicated by two pink corners). For example:

1. Write your R so that it shows as desired as symbol for the real 
numbers (you are now inside the \mathbb inset)
2. Press the right arrow key (to move out of the \mathbb inset)
3. Type \aleph_0

I hope this helps!

Daniel