\begin{definition}[Definition:Derivation on Ring]
Let $R$ be a ring.
A '''derivation''' on $R$ is a group homomorphism $D$ of the additive group of $R$ which satsfies the Leibniz law:
:$\forall a, b \in R: \map D {a b} = \map D a b + a \map D b$
\end{definition}