From the Publisher
'.... the piano accompaniment proposed in a separate and complete book, deliberately of a very accessible level, can be added to enrich either a practice session or a public performance. However, one will note that, in essence, it remains optional and that the original duo parts are musically sufficient on their own.' Jean-Marc Allerme
Difficulty level, roughly compared to ABRSM exam grades. 0 is beginner, 9 is advanced (beyond grade 8).