John D. MacDonald

alternate reality n.	1950 J. D. MacDonald Shadow on Sand in Thrilling Wonder Stories Oct. 27/1 We have made the basic and very important discovery of a twin planetary system corresponding to our own, separated from us only by a symbolic logician’s definition of reality. This is not a completely physical and technical phenomenon. It is a philosophical phenomenon. In simplest terms the formula can be expressed this way: The twin world exists because any definitive explanation of reality presupposes alternate realities. Thus the doorway was achieved by the creation of unreality. Call it negative matter if you will. A sphere where there is no reality must, through the application of the basic formula, be a bridge between realities.
three-D n.	1948 J. D. MacDonald School for the Stars in Astounding Science Fiction Oct. 110/1 You must have loaned your three-di projector, too. All you’ve got here is the micrograph projector for your dirty two-dimensional scenes.