I'm trying to get through Spivak's Calculus on my own and even though I kinda understand induction I'm not so sure that's the case when it comes to complete induction. So I tried to do a starred problem which involves using it. But I'm not sure that my proof is valid, can someone check this for me?
So the problem is that I have to prove that
For every natural $n>1$, if $n$ is not prime we can write it as a product of primes.
I'm starting with a base case. For $n=2$, $n$ is prime, so the assumption holds.
Let's assume that for some $n > 1$ and also all numbers $p <= n$ the assumption holds.
Then $n+1 = cd$. If $n+1$ is not prime, then $c < n+1$ and $d < n+1$, but as they are natural numbers, we can also write that $c <= n$ and $d <= n$. But we assumed that if $p <= n$, and $p$ is not prime, we can write it as a product of primes. So if $c$ or $d$ are not primes, we can write them as a product of primes. That means that $n+1$ can be written as a product of primes if it's not prime, which completes the proof.