assignTeam(string uid, string id, string studentId, string teamId) {
  assume exists //accounts/account[uid]/tutor[id]/group[//exercises/exercise[id]/student[studentId]/group];
    # implies the existence of the student, the exercise, the group and enough rights by a tutor account
 
  assume not exists //exercises/exercise[id]/student[studentId]/team;
 
  update //exercises/exercise[id]/student[studentId]/team teamId;
}