We analyzed the first stage of our construction, confined to two-dimensional space, and found it to be as durable and resistant as the earth itself. … - El Lissitzky

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We analyzed the first stage of our construction, confined to two-dimensional space, and found it to be as durable and resistant as the earth itself. We build in this space just as we would on the ground, and therefore must take as our point of departure the concepts of gravity and force of attraction, as the foundation of everything built on the land. In PROUN the reciprocity of the effects of gravity [Newton, 'for every action an equal and opposite reaction'] manifests itself in a new capacity. We see that on the surface (plane) of the picture, the PROUN ceases to exist as such and becomes a building surveyed from every direction — considered from above or examined from below. The result of this turns out to be the destruction of the single axis that leads to the horizon.