. . . and ones that are unusually easy to play.[citation needed]"Yes, citation needed indeed...
Like this one?
If you look through the history tab on the WP page, a few years ago this sentence ended: "...and études that required unusually facile technique." I am still not entirely clear what this means, but it might make sense. Someone who understands even less than I do has changed it to nonsense, as so often happens at WP.