A natural transformation $\alpha \colon F\Rightarrow G$ from $F$ to $G$ is a transformation
\[ \webleft\{ \alpha _{A}\colon F\webleft (A\webright )\to G\webleft (A\webright )\webright\} _{A\in \text{Obj}\webleft (\mathcal{C}\webright )} \]
from $F$ to $G$ such that, for each morphism $f\colon A\to B$ of $\mathcal{C}$, the diagram
commutes.
