# Derivation

Let $R$ be a commutative unital ring (resp. sheaf of commutative unital rings). A derivation of $R$ is a map $D: R \to R$ (resp. a sheaf-theoretic map from $M$ to itself) such that:
• $D$ is $R$-linear (viz, its a map of $R$-modules)
• $D(f) = f(Dg) + (Df)g$