Mencari Kata Yang salah

procedure TForm2.Button1Click(Sender: TObject);
var a:TStringList ; i:integer ;
begin
a:= TStringList.Create ;
a.Delimiter := ' ';
a.DelimitedText := Memo1.Text ;

for I := 0 to a.Count -1 do begin
  ListBox2.ItemIndex:= ListBox2.Items.IndexOf(a[i]) ;
  if ListBox2.ItemIndex = -1 then
  ListBox1.Items.Add(a[i]) ;

end;
end;