private void openList()
 {
     ListeLecture window_list = new ListeLecture(this);
     window_list.Owner = this;
     window_list.Show();
     this.Hide();
 }
 private void openBib()
 {
     ListeLecture window_bib = new ListeLecture(this);
     window_bib.Owner = this;
     window_bib.Show();
     this.Hide();
 }