Arithmetic modulo 2 is all about odd vs. even. The even integers correspond to remainder 0 when dividing by 2, and the odds have remainder 1 when dividing by 2.

The most familiar form of modulo math is the clockface. Ten hours from four o’clock is two o’clock, not fourteen o’clock; this is an example of arithmetic modulo twelve.

You may never have heard of modular arithmetic, but you use it every day without the slightest difficulty. In this system, numbers wrap around when they reach a certain size called the modulus; it ...