grantExaminerRights(ident uid, ident username, ident examId) {
  assume exists //accounts/account[uid]/admin;
 
  assume exists //accounts/account[username]; # implicitly true in OO implementations
  assume exists //exams/exam[examId];
 
  assume not exists //accounts/account[username]/examiner[examId]);
  assume not exists //exams/exam[examId]/examiner[username]); # implied by integrity and the assumption before
 
  insert //accounts/account[username] <examiner exam=[examId] />;
  insert //exams/exam[examId] <examiner account=[username] />;
}