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 ofpolynomials 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 $R$.