= Skew polynomial ring of an automorphism
{title2=$A[t;\sigma]$}
For an <automorphism> $\sigma$ of a unital <ring> $A$, this <ring> consists of finite sums $\sum_{j\geq0}a_jt^j$, with multiplication determined by $ta=\sigma(a)t$. Both left and right coefficient normal forms are available because $\sigma$ is invertible. The <noncommutative Hilbert basis theorem> implies that it is a <right Noetherian ring> when $A$ is, and a <left Noetherian ring> when $A$ is. Invertibility of $\sigma$ matters in this two-sided formulation.
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