# Notting off

 The simplest element of digital logic is the inverter. An inverter takes a logical value as input and produces another value as output. There are two possible logical values. Sometimes they are called "true" and "false". Other times they are called "0" and "1". In digital logic something corresponds to true, something else to false. In the game we are looking at now, the presence of a glider represents a logical true, the absence of a glider represents a logical false.
 The inverter is made on the cannon on the left and the structure to its right. The input to the inverter comes from the bottom, the output leaves to the right. There are also three corner turners to steer gliders from the output back to the input. When no gliders (false) enters from the bottom, then gliders exit at the right (true). When gliders enter at the bottom, no gliders leave.
 This inverter is made of little squares. Inverters can, and have, been made of transistors, vacuum tubes, hydraulics, strings and pulleys, and tinker toys. The material doesn't matter. It's an inverter as long as a "true" input produces a "false" output and vice versa.

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Brian Silverman