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