function sm2(interval, ef, streak, grade) {
  if (grade >= 3) {
    if (streak == 0) {
      interval = 1
      streak = 1
    } else if (streak == 1) {
      interval = 6
      streak = 2
    } else {
      interval = Math.round(interval * ef)
      streak++
    }
  } else {
    interval = 1
    streak = 0
  }

  ef = calcEase(ef, 0)
  ef = ef < 1.3 ? 1.3 : ef

  return {
    streak,
    interval,
    ef
  }
}

function calcEase (oldEf, grade) {
  return (-0.02 * Math.pow(quality, 2)) + (0.28 * quality) + (oldEase - 0.8)
}

procedure Repetition(ElementNo,Grade:longint;var NextInterval:longint;commit:WordBool);
var DataRecord:TDataRecord;
begin

  DataRecord:=GetDataRecord(ElementNo);
  with DataRecord do begin
  if Grade>=3 then begin
  if Repetition=0 then begin
  Interval:=1;
  Repetition:=1;
  end
  else if Repetition=1 then begin
  Interval:=6;
  Repetition:=2;
  end
  else begin
  Interval:=round(Interval*EF);
  Repetition:=Repetition+1;
  end;
  end
  else begin
  Repetition:=0;
  Interval:=1;
  end;
  EF:=EF+(0.1-(5-Grade)*(0.08+(5-Grade)*0.02));
  if EF<1.3 then
  EF:=1.3;
  NextInterval:=Interval;
  end;
  if commit then
  SetDataRecord(ElementNo,DataRecord);
  end;