Comparison between two select_multiple answers arrays

I would like to perform a verification between two select_multiple questions. I'll explain the scenario:

Question 1 will provide the user with several options of methods for him/her to tell which of them were used in the field:

  • Method A ;
  • Method B ;
  • Method C ;
  • ...

Question 2 will also allow the user to choose the same alternatives. However, this time he/she should inform which of the methods used were effective:

  • Method A ;
  • Method B ;
  • Method C ;
  • ...

My wish in this case is to prevent the user from adding an alternative in Question 2 that was not selected in Question 1.

As a solution, I've thought of a constraint like:
if(selected(${question_2}, 'A'), selected(${question_1}, 'A') = true(), true()) and if(selected(${question_2}, 'B'), selected(${question_1}, 'B') = true(), true()) and if(selected(${question_2}, 'C'), selected(${question_1}, 'C') = true(), true()) and ...

But it seems difficult to understand, implement and change, if necessary.
Is there any better alternative to achieve this result?

Thanks for the support! :blush:

perhaps something like this is a bit clearer (?):

if ((selected(${question_2}, 'A') and not(selected(${question_1}, 'A'))) or (selected(${question_2}, 'B') and not(selected(${question_1}, 'B'))) or ... , "Error", "OK")

bascially it checks for mismatches, when you've selected an option in question2 that's not selected in question1.