Hello!!
I want to prove the following lemma:
Let $F[t,t^{-1}]$ be the ring of the polynomials in $t$ and $t^{-1}$ with coefficients in the field $F$ and assume that the characteristic of $F$ is zero.
Then for any $n$ in $F[t, t^{-1}]$, $n$ is a nonzero integer if and only if
- $n$ divides $1$
- either $n-1$ divides $1$ or $n+1$ divides $1$, and
- there is a power $x$ of $t$, so that $\dfrac{x-1}{t-1}\equiv n \pmod {t-1}$
Is the proof as follows?
From an other lemma we have that $(t^n-1)/(t-1)\equiv n \pmod {t-1} \tag {1}$.