Functional Dependencies in Relations
While I'm unaware that your suggested rule has a name and couldn't find it in any texts on my shelf, it's a consequence of reflexivity and transitivity, as you probably know already. Here's how:
$$
\begin{align}
ACDE &amp;\rightarrow A &amp;\text{(reflexivity)}\\
A &amp;\rightarrow B &amp;\text{(hypothesis)} \\
ACDE&amp;\rightarrow B &amp;\text{(transitivity)}
\end{align}$$