Question

For example I only want to see the classes that got code in BOTH syp and cus layers in my project.

Answer 1

SQL comes to your rescue:

static void UtilElement2Layers(Args _args)
{
    UtilIdElements uc, u1, u2;
    while select uc
        where uc.recordType == UtilElementType::Class
        exists join u1
        where u1.parentId == uc.id
           && u1.utilLevel == UtilEntryLevel::cus
        exists join u2
        where u2.parentId == uc.id
           && u2.utilLevel == UtilEntryLevel::syp
        // && u2.id == u1.id
    {
        info(uc.name);
    }
}