A
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FE (→GE,EE) added an unobvious cautionary 
to a in the 2nd crotchet. It suggests that it was Chopin who performed it, since a few other situations prove the composer's subconscious uncertainty as to the validity of a 3rd key signature 
, e.g. the mistake in b. 231.
Compare the passage in the sources »
category imprint: Differences between sources
issues: Cautionary accidentals, Authentic corrections of FE
notation: Pitch