Let $\mathcal{C}$ be a $k$-linear abelian category. Are the following two definitions of enough projectives equivalent?
(i) For every object $A$ there exists a projective object $P$ s.t. $P\twoheadrightarrow A$
(ii) Every simple object $U_i$ has a projective cover $p_i: P_i\twoheadrightarrow U_i$
The first one is taken from wikipedia, the second from the book Tensor Categories by Etingof et al.
I think this cannot be the same, for the superficial reason that nothing in (ii) makes a reference to arbitrary (generally indecomposable) objects of $\mathcal{C}$. However, I might be very wrong since I cannot seem to prove it.
Any pointers?
They do not, in general. I bet Etingof is assuming we're in a semisimple category, as is usually the case, if not always, in that book. If every object is a sum of simples, then it should be clear that these conditions are equivalent, since a sum of projectives is projective and a sum of epis is epi. The conditions are not equivalent in general, since abelian categories need not have any simple objects. See Jeremy Rickard's example here.