Help me define my use case in OPL. In my system, I have users and merchants, a user (example user-x) can belong to a group (group-y). A merchant (example merchant-z) can be created by a user. some of the groups that will exist can be "systemAdmins" and "superAdmins", any user that exists in the "systemAdmins" group has the permission to "createMerchant".