Chopin Etude Op. 9 No. 2 In the 13th full bar, Right hand 5th note. My music sheet shows a Cb (equivalent to B). Should it be there? Should it be played as B natural followed by B-flat?
In keeping with the melodic and rhythmic elements Chopin is working with, his intention is to flatten the sixth degree of Eb (key) - i.e., the C. This happens to be the enharmonic equivalent of B. Regardless, his intentions lead him to write Cb.
This is an idiosyncratic feature of the key of Eb. Flattening the sixth of other major scales does not lead to this sort of enharmonic equivalent ambiguity.
EDIT As Matt points out in the comments, the same ambiguity arises if Ab major, where the 6th is F.