A
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Taking into account the three previous similar phrases in this bar and d
2 in AsI, one could assume an oversight of a 
in A. However, it seems more likely that Chopin consciously changed the pitch of this note:
- Chopin would often omit accidentals to notes belonging to the current key; however, he would rarely overlook an accidental supposed to define the alteration (only a few times in his entire oeuvre);
- Chopin did not correct the possible mistake while proofreading FE, despite the fact that he changed slurs in this very bar.
Compare the passage in the sources »
category imprint: Differences between sources; Corrections & alterations
issues: Main-line changes
notation: Pitch