# Euclid's Lemma for Prime Divisors/General Result/Proof 3

## Lemma

Let $p$ be a prime number.

Let $\displaystyle n = \prod_{i \mathop = 1}^r a_i$.

Then if $p$ divides $n$, it follows that $p$ divides $a_i$ for some $i$ such that $1 \le i \le r$.

That is:

$p \divides a_1 a_2 \ldots a_n \implies p \divides a_1 \lor p \divides a_2 \lor \cdots \lor p \divides a_n$

## Proof

Let $p \divides n$.

$\forall i \in \set {1, 2, \ldots, r}: p \nmid a_i$
$\forall i \in \set {1, 2, \ldots, r}: p \perp a_i$
$p \perp n$

By definition of coprime:

$p \nmid n$

The result follows by Proof by Contradiction.

$\blacksquare$

## Source of Name

This entry was named for Euclid.