Question: value is not effective for activating Composition of operation %Nabla

I read  help document of %Nabla :

%Nabla is the inert form of Nabla, that is: it represents the same mathematical operation while holding the operation and checking of arguments unperformed. The expansion rules defined for Nabla, however, also work (are implemented) for the inert %Nabla. To activate the operation use value.



But if I want to use Composition function , is it not useful? why? how to do?


we know that:



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