definition user {}

definition group_type {
    relation type: group
}

definition group {
    relation member: user
    relation type_of: group_type

    permission can_post = member + type_of#type1
}

---

group:group1#member@user:user1
group:group1#type_of@group_type:type1

I know this is not correct but how would I express something like this?