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Published online by Cambridge University Press: 22 February 2017
For a von Neumann subalgebra   $A \, \subseteq \, {\cal B}({\cal H})$  and any two elements a, b ∈ A with a normal, such that the corresponding derivations d a  and d b  satisfy the condition ‖d b (x)‖ ≤ ‖d a (x)‖ for all x ∈ A, there exist completely bounded (a)ʹ-bimodule map
 $A \, \subseteq \, {\cal B}({\cal H})$  and any two elements a, b ∈ A with a normal, such that the corresponding derivations d a  and d b  satisfy the condition ‖d b (x)‖ ≤ ‖d a (x)‖ for all x ∈ A, there exist completely bounded (a)ʹ-bimodule map   $\varphi : {\cal B}({\cal H}) \rightarrow {\cal B}({\cal H})$  such that d b |A = φ d a |A=d a φ|A. (In particular d b (A) ⊆ d a (A).) Moreover, if A is a factor, then φ can be taken to be normal and these equalities hold on
 $\varphi : {\cal B}({\cal H}) \rightarrow {\cal B}({\cal H})$  such that d b |A = φ d a |A=d a φ|A. (In particular d b (A) ⊆ d a (A).) Moreover, if A is a factor, then φ can be taken to be normal and these equalities hold on   ${\cal B}({\cal H})$  instead of just on A. This result is not true for general (even primitive) C*-algebras
 ${\cal B}({\cal H})$  instead of just on A. This result is not true for general (even primitive) C*-algebras   ${\cal A}$ .
 ${\cal A}$ .