I wrote the attached model below, but I got an infeasible integer solution and am working on debugging the model. Thesis Model Replication.gms (9.78 KB)
In the pre-solve stage, I got the below error.

So, I thought I was missing indicating in the constraint that (j, i)∈A_j^- and j ∈ S. My question is, how to write these two conditions in the constraint?

But when I’m using the dollar option, it gives me error 148.

I couldn’t be familiar in your code, but, as I know, if you want to use a set indices in the $ condition, you should use with “ord”.
For example;

sum(i$(ord(AMinus) > 5), x(i,j)) .....etc

Because you defined “AMinus” as a set. (but, still, I am not quite sure this is what you mean)
But, I dont know how you can write the condition for “∈”.

Send you entire model, so we can reproduce. Looking at the equation in isolation makes no sense. We don’t even know what Aminus is in your code. -Michael