Is_in_list function?

Dear all,

I'm creating a rather complex form and some of the branching (skipping questions) is based on earlier input.

In the first questions (q1) which is a select_one question, input is received where the name is between a to z. (the label has a longer description, but the name is just 1 character).

Then in later questions, I only want to show that question the input on the first question was a, f, r, v or z. And on another questions, should only be shown when the input on the first question was b, l, r, v, z.

Obviously, I can use a formula like this in the relevant columns:

${q1} = 'a' or ${q1} = 'f' or ${q1} = 'r' or ${q1} = 'v' or ${q1} = 'z'

but that seems rather long and complicated, specially if e.g. 13 of the 26 character need to be included/excluded, the formula will get very long.

Therefor, I have been looking for a function that would be more or less the opposite of selected-at or something like "in-list()", is-member() or instr(), where I could put for example instr('afrvz', ${q1}) but I have not been able to find anything.

As the exact set of characters in the 'relevant' column can be different per question, using a calculate first will work, but will not make it more efficient.

Is there a short and elegant solution that I missed? Or is there a work-around for it?

(I spend quite some time searching but without much luck)

Thanks for your support in advance,