People being able to push open doors is often just a bad idea. Collisions can occur if the door is solid and some doors are better left without any apertures (eg public lavatories).
Today’s invention is a door which can only be opened by pulling (irrespective of your direction of travel).
There are two parts to the image.
Each part is a plan view of the edge of a door and the direction controller mechanism.
In the lower part, the door is locked by the interference between the two prongs on the cylinder joining the handles and the two triangular blocks attached to the wall. The cylinder and prongs are sprung so as to naturally return to this position when the handle is released.
To open the door from the right hand side (upper diagram), rotate the handle clockwise so that the left prong points downwards and can then be pulled past the left triangular block (which is lower on the wall than the right block). This handle is attached to the cylinder via a ratchet which can only drive the cylinder when the handle turns clockwise.
Releasing the handle allows the cylinder to rotate back to its normal orientation. The door then moves back to its central position, driven by a normal door closer spring.
As it moves back, the left prong bypasses the right (upper) triangle and hits the left (lower) triangle, so that its face acts as a ramp and allows the left prong to slip over and into the equilibrium position.
Similar logic applies to opening the door from the left side.