yes, sorry, my fault, this is correct:
...
filter tSubStackList with (tFirstCharacter & "*")
## = remove ALL lines that do NOT start with tFirstCharacter
...
The placeholder * stands for "any other character(s)".
Nonot 2 with the same first character in name
or not 2 with the same name ?
If I can not use more than once substack with the same first character, there is no point to take it as a reference! No?

That what I meant with:
In that case there is no way to differ these stacks from just the first character, it the first character is identical, right?If you have prepared everything correctly (NOT 2 substacks with the same first character in name etc...)

Best
Klaus