English: Excerpt of Nocturne Op. 15, no. 2 by Frédéric Chopin. This example demonstrates the challenges one frequently encounters in Optical Music Recognition: ambiguity and violations of musical syntax. The dot in the red box on the lower staff is to the right of a notehead as well as below a notehead and could be associated with both of them. The correct association is with the left notehead, because the alternative hypothesis would not make any sense, musically speaking. Similarly, the number of notes in the last measure (green box on upper staff) might be mistaken as exceeding the meter, resulting in an invalid number of notes in that measure. The musical notation includes an unusually complex tempo in 2 layers. The notation 5 in the arc above the notes in the treble clef in the preceding measure signals a quintuplet, 5 notes to be played over the same duration as 4 notes in the bass clef. Variations of this quintuplet are a thematic element of the piece. This 1915 Schirmer printing reflects Rafael Joseffy’s editing of the 1881 scores by Dr. Theodore Kullak that attempts to show additional interpretive nuances. In the measure shown the 4 underneath the arc in the treble clef and the 3 underneath the arc in the bass clef indicate that the 4 and the 3 should be played in the same interval. The 1881 score(s) don’t indicate this interpretive hint, only the quintuplet. See the footnotes on the 1st page of this nocturne in the 1881 Instructive Edition Of Chopin’s works, Volume V page 18 for further explanation and note the explicitly different interpretation. The complexity of Chopin’s works were difficult for both the composer and his contemporaries to capture in musical notation, frequently resulting in scores that are visually intimidating and complex.