changeResult(string uid, string id, string studentId, string taskId, double points) {
  assume exists //accounts/account[uid]/examiner[id];
 
  assume exists //exams/exam[id]/results/participant[studentId];
  assume exists //exams/exam[id]/tasks/task[taskId];
 
  assume points >= 0 && points <= //exams/exam[id]/tasks/task[taskId]/maxPoints;
 
  assume exists //exams/exam[id]/results/participant[studentId]/result[taskId];
 
  update //exams/exam[id]/results/participant[studentId]/result[taskId]/points points;
}