Violin and viola - difficult - Digital Download SKU: S9.Q6641 For Violin and Viola. Composed by Heinz Holliger. This edition: score and parts. Downloadable, Score and parts. Duration 12 minutes. Schott Music - Digital #Q6641. Published by Schott Music - Digital (S9.Q6641). In the Mozart Year, Thomas Zehetmair and Ruth Kilius asked Heinz Holliger for a striking encore piece for violin and viola for Mozart's Sinfonia concertante which had often been performed by them under his direction. The outcome, however, is an independent three-part cycle consisting of quite different pieces. The first has been woven exclusively out of floating harmonics, the second is a wild whirling dance, while the third condenses into a six-part chorale in which each player has to sing a third voice in addition to playing double stops on his string instrument.