  Let A be an exact category, that is, an extension-closed full subcategory of
an abelian category. Firstly, we give some necessary and sufficient conditions
for A to have almost split sequences. Then, we study when an almost split
sequence in A induces an almost split sequence in an exact subcategory C of A.
In case A has almost split sequences and C is Hom-finite Krull-Schmidt, this
provides a necessary and sufficient condition for C to have almost split
sequences. Finally, we show two applications of these results.
