How come? This is my model so far:

definition company {
    relation employee_viewer: permission_group#membership
    relation employee_direct_reports_viewer: permission_group#membership
    permission view_direct_reports_employees = employee_direct_reports_viewer
    permission view_employees = employee_viewer
}

/** employee represents an employee. */
definition employee {
    relation is_self: employee
    relation parent_company: company
    relation leader: employee
    permission view = is_self + parent_company->view_employees + parent_company->view_direct_reports_employees & leader
}

/** permission_group represents a permission group. */
definition permission_group {
    relation member: employee
    permission membership = member
}