pasting the schema again just so it is close by

yaml
definition user {}

definition group {
    relation member: user
}

definition prompt {
    relation creator: user
    relation editor: user
    relation viewer: user | group#member
    permission can_view = creator + editor + viewer
    permission can_edit = creator + editor
}

i am interested in finding all subjects with the

viewer

relation that has that relation via group membership