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b. 10-12

composition: Op. 28 No. 4, Prelude in E minor

2 slurs in As

2 slurs in A (→FC)

2 slurs in GE

Slur in FE

..

The longer slur of As is probably the initial version, concerning the crossed-out version of the melodic line in b. 10-11. It is indicated by a second slur between b. 11-12, which begins only just over the a1 crotchet, added (or left) as valid after corrections.
It most probably means that the second slur was also added only after those corrections, probably with intent to replace the first, longer slur with it.
The missing slur in b. 11-12 in FE (→EE) is a mistake of the engraver; in turn, leaving the grace note in b. 11 out of the slur in GE and adding a little slur combining that grace note with the crotchet in EE are editorial revisions.

category imprint: Differences between sources; Corrections & alterations; Source & stylistic information

issues: EE revisions , Errors in FE , GE revisions

b. 11

composition: Op. 28 No. 4, Prelude in E minor

c-e-a in As, A (→FC,FEEE) & CGS

B-d-a in GE

..

The fact that the chord was not changed in the middle of the bar must be a mistake of the engraver of GE.

category imprint: Differences between sources

issues: Errors in GE

b. 11-19

composition: Op. 28 No. 4, Prelude in E minor

..

Both in b. 11 and 19, the grace notes in A (→FEEE) are non-slashed, whereas in FC (→GE) – slashed. It is an inaccuracy that would often happen to Fontana-copyist, in this case almost certainly contrary to the intention of Chopin. The Chopinesque entries in FED equate the grace note and the crotchet with two quavers, which can be considered one of the performance possibilities of these motifs. We recommend a slightly shorter grace note, which could be written down as .
We give the variants resulting from the above differences of notation in the notes to b. 10-11 and 18-19.

category imprint: Differences between sources; Source & stylistic information

issues: Annotations in teaching copies , Annotations in FED , Non-slashed grace notes , Fontana's revisions

b. 12

composition: Op. 28 No. 4, Prelude in E minor

Fingering written into FED, FEJ & FES

No teaching fingering

..

In three out of four teaching copies, we find identical Chopinesque entries, indicating a swap of fingers on the c1 note (from 1st to 2nd). The entry in FED is clearest, whereas the one in FEJ – most difficult to read.

category imprint: Graphic ambiguousness; Differences between sources

issues: Annotations in teaching copies , Annotations in FED , Annotations in FES , Annotations in FEJ

b. 12

composition: Op. 28 No. 4, Prelude in E minor

Fingering written into FES

No teaching fingering

..

The poorly legible addition in FES, performed in pencil, most probably marks fingering – it contains two marks, out of which the first is almost certainly a digit '3', which makes us suppose that the second will be a digit too, which we thereby interpret as a '5'. According to us, a similarly placed entry in FEJ, however, does not mark fingering, but a variant in the form of an f1 grace note. 

category imprint: Differences between sources

issues: Annotations in teaching copies , Annotations in FES