A, B, C, D, F or G, so ... (4)

I believe the answer is:

note

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'so' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for note that I've seen before include "Symbol in a score" , "Eminence" , "Jotting" , "Write down" , "Musical tone" .)

I've seen this clue in The Sun.

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