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