# Division Theorem/Positive Divisor/Uniqueness/Proof 2

## Theorem

For every pair of integers $a, b$ where $b > 0$, the integers $q, r$ such that $a = q b + r$ and $0 \le r < b$ are unique:

$\forall a, b \in \Z, b > 0: \exists! q, r \in \Z: a = q b + r, 0 \le r < b$

## Proof

It is given by Division Theorem: Positive Divisor: Existence that such $q$ and $r$ exist.

Let $a = q b + r$ where $q, r \in \Z$ and $0 \le r < b$.

Thus:

$\dfrac a b = q + \dfrac r b$

and:

$0 \le \dfrac r b \le \dfrac {b - 1} b < 1$

So:

$q = \floor {\dfrac a b}$

and so:

$r = a - b \floor {\dfrac a b}$

Thus, given $a$ and $b$, the numbers $q$ and $r$ are unique determined.

$\blacksquare$