skew polynomial ring

If $(\sigma,\delta)$ is a left skew derivation on $R$ , then we can construct the (left) skew polynomial ring $R[\theta;\sigma,\delta]$ , which is made up of polynomials in an indeterminate $\theta$ and left-hand coefficients from $R$ , with multiplication satisfying the relation

\theta\cdot r=\sigma(r)\cdot\theta+\delta(r)

for all $r$ in $R$ .