  Are all subcategories of locally finitely presentable categories that are
closed under limits and $\lambda$-filtered colimits also locally presentable?
For full subcategories the answer is affirmative. Makkai and Pitts proved that
in the case $\lambda=\aleph_0$ the answer is affirmative also for all iso-full
subcategories, \emph{i.\thinspace e.}, those containing with every pair of
objects all isomorphisms between them. We discuss a possible generalization of
this from $\aleph_0$ to an arbitrary $\lambda$.
