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# Divisibility

<https://en.wikipedia.org/wiki/Divisibility>

Divisibility := If `a` and `b` are ints, then `a` divides `b` if `b = a*n` for some int `n`. `a` is called a *factor* or *divisor* of `b`. `b` is called a *multiple* of `a`.

* shorthand `a divides b` is `a | b` i.e. `divisor | multiple`
* (ab e Z AND b=a\*n) . a | b
* int `p` is even exactly when `2 | p`
* zero being even is a special case cuz zero is divisible by any int