By Joshua Cohen, from Book of Numbers, out next month from Random House. Cohen is a contributing editor of Harper’s Magazine.

Toward the end D-Unit had been working on the touchscreen. Do not interrupt, we do not digress. Tactiles. Haptics. It must have been that he was forced into this, or the PARC touchscreen group had been short an engineer and asked him and he could not refuse, D-Unit could never refuse. But his true cur, toward the end, was printing, still printing, but not in 2-D anymore, in 3-D, and he would have printed in 4-D if he…