  A theorem of Keller states that the Yoneda algebra of the simple modules over
a finite-dimensional algebra is generated in cohomological degrees $0$ and $1$
as a minimal $A_\infty$-algebra. We provide a proof of an extension of Keller's
theorem to abelian length categories by reducing the problem to a particular
class of Nakayama algebras, where the claim can be shown by direct computation.
