code: func (cps ComparablePrincipalSet) ToPrincipalSet() policies.PrincipalSet {
  	var res policies.PrincipalSet
  	for _, cp := range cps {
  		res = append(res, cp.principal)
  	}
  	return res
  }
docs: // ToPrincipalSet converts this ComparablePrincipalSet to a PrincipalSet