# A Logic Gate Made of People

“I don’t know your names,” Von Neumann said, tapping the shoulders of two of the soldiers. “The two of you will be responsible for signal input, so I’ll call you ‘Input 1’ and ‘Input 2.’” He pointed to the last soldier. “You will be responsible for signal output, so I’ll call you ‘Output.’” He shoved the soldiers to where he wanted them to stand. “Form a triangle. Like this. Output is the apex. Input 1 and Input 2 form the base.”

“You could have just told them to stand in the Wedge Attack Formation,” Qin Shi Huang said, glancing at Von Neumann contemptuously.

Newton took out six small flags: three white, three black. Von Neumann handed them out to the three soldiers so that each held a black flag and a white flag. “White represents 0; black represents 1. Good. Now, listen to me. Output, you turn around and look at Input 1 and Input 2. If they both raise black flags, you raise a black flag as well. Under all other circumstances, you raise the white flag.”

“I think you should use some other color,” Qin Shi Huang said. “White means surrender.”

The excited Von Neumann ignored him. He shouted orders at the three soldiers. “Begin operation! Input 1 and Input 2, you can raise whichever flag you want. Good. Raise! Good. Raise again! Raise!”

Input 1 and Input 2 raised their flags three times. The first time they were black-black, the second time white-black, and the third time black-white. Output reacted correctly each time, raising the black flag once and the white one twice.

“Even an idiot would be capable of that. Tell me, what are they really doing?” Qin Shi Huang looked baffled.

“The three soldiers form a computing component. It’s a type of gate, an AND gate.” Von Neumann paused to let the emperor digest this information.

Qin Shi Huang said impassively, “I’m not impressed. Continue.”

Von Neumann turned to the three soldiers again. “Let’s form another component. You, Output: if you see either Input 1 or Input 2 raise a black flag, you raise the black flag. There are three situations where that will be true: black-black, white-black, black-white. When it’s white-white, you raise the white flag. Understand? Good lad, you’re really clever. You’re the key to the correct functioning of the gate. Work hard, and the emperor will reward you! Let’s begin operation. Raise! Good, raise again! Raise again! Perfect. Your Imperial Majesty, this component is called an OR gate.”

Then, Von Neumann used the three soldiers to form a NAND gate, a NOR gate, an XOR-gate, an XNOR-gate, and a tristate gate. Finally, using only two soldiers, he made the simplest gate, a NOT gate, or an inverter: Output always raised the flag that was opposite in color from the one raised by Input.

Von Neumann bowed to the emperor. “Now, Your Imperial Majesty, all the gate components have been demonstrated. Aren’t they simple? Any three soldiers can master the skills after one hour of training.”

## Notes:

Used to build a computer out of an army.

Folksonomies: computer science unplugged

Taxonomies:
/law, govt and politics/armed forces/army (0.573597)
/society/unrest and war (0.443110)
/technology and computing/mp3 and midi (0.264441)

Keywords:
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Entities:
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Concepts:
Logic gate (0.951095): dbpedia | freebase
OR gate (0.879267): dbpedia | freebase | opencyc | yago
NOR gate (0.879267): dbpedia | freebase | yago

The Three-Body Problem
Books, Brochures, and Chapters>Book:  Cixin, Liu (2014-11-11), The Three-Body Problem, Macmillan, Retrieved on 2015-03-05