The big question is what comes after the F9?

Just looking at the C to F9 I would surmise it to be 1/2 step changes.
The C chord - C_E_G to a F9 - F_A_C_Eb_G have the common notes C and G and the 1/2 step change would be the E to the Eb.

JonD and I do this a lot. We look for chord changes that have common notes with one or more notes changing only a 1/2 step. This is done regardless of the key signature.


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