Let C be an additive category with an involution *. Suppose that ? : X ? X is
a morphism of C with core inverse ?# : X ? X and ? : X ? X is a morphism of
C such that 1X + ?#? is invertible. Let ? = (1X+?#?)-1, ? = (1X+??#)-1, ?
= (1X-??#)??(1X-?#?), ? = ?(1X-?#?)?-1??#?,? = ??#??-1(1X-??#)?,? =
?*(?#(*?*(1X-??#)?. Then f = ? + ? ? ? has a core inverse if and only if
1X-?, 1X-? and 1X-? are invertible. Moreover, the expression of the
core inverse of f is presented. Let R be a unital *-ring and J(R) its
Jacobson radical, if a ? R# with core inverse a # and j ? J(R), then a + j ?
R# if and only if (1-aa#)j(1+a#j)-1(1-a#a) = 0. We also give
the similar results for the dual core inverse.