For Banach spaces X,Z, let
B(X,Z) denote the space of bounded linear operators from X into Z and K(X,Z)
(resp. W(X,Z)) the subspace of compact (resp. weakly compact) operators. It
is shown that (a) if X contains an isomorph of c0, then K(X,l∞) is not
complemented in B(X,l∞), (b) if S is a compact Hausdorff space which is
not scattered, then K(C(S),Z) is not complemented in W(C(S),Z) for
Z = c0 or l∞. In particular, K(l∞,c0) is not complemented in B(l∞,c0),
which gives a negative answer to a question proposed by Arterburn and
Whitley.
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