### Why use this resource?

Once students are clear about the fact that if a prime number \(p\) divides the product \(ab\) then \(p\) divides \(a\) or \(p\) divides \(b\), they can go on to show that every integer has a unique prime factorisation. This resource gives the steps of a proof, but students have to sort them into the right order. This is a good way to practise working with a more sophisticated proof than most students would come up with themselves at this stage, and gives students the chance to get used to a more formal style of language and argument.