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Completely bounded maps on $$C^*$$-algebras and invariant operator ranges. (English) Zbl 0554.46028
Wittstock used deep results on $$W^*$$-algebras and a Hahn-Banach theorem for set-valued matrix sublinear functionals to prove that the completely positive maps from a $$C^*$$-algebra into L(H) span the completely bonded maps. The author presents an elementary proof of this based on Arveson’s extension theorem. He also derives an equivalent reformulation of the invariant operator range problem.
Reviewer: P.G.Spain

##### MSC:
 46L05 General theory of $$C^*$$-algebras 47A15 Invariant subspaces of linear operators
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