Visible in A over the triplet in bars 17 and 21 are erasures that point to corrections made by Chopin in those places. It is hard to give an obvious explanation as to what was being changed, yet it seems probable that Chopin was removing a numeral and a slur defining the triplet (moving the slur under the triplet and extending it one note further) to insert a motivic long accent instead.
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category imprint: Corrections & alterations; Source & stylistic information
issues: Corrections in A
notation: Pitch