Double-leaf windows, symmetrical horizontal division 50-50 with a movable mullion

Double-leaf windows with a horizontal symmetrical division 50-50 with a movable mullion. The leaf widths are the same. The movable mullion is one of the elements of the window structure, permanently connected to one of the sash frames. This makes it possible to divide the window with the sashes closed, but after opening them, it allows free use of the non-divided space.