Bottomless white cubic box.
At first sight, you would see a black square, linked to the canvas by four straight lines. But if you insist and take the title for granted, then you might start to see a bottomless white cubic box. If you see it, then I successfully persuaded you that it exists. I forced your own perception. Now that I convinced you, you won’t see anything else but a bottomless white cubic box. The paradox is that The bottomless white cubic box, is a present artefact which is actually absent. The painting is itself present, as a canvas, but there is no such thing as a bottomless white cubic box.