Postmodernism in music may be hard to define – even harder than the same notoriously slippery term in literature – but Olga Neuwirth's viola concerto Remnants of songs … an Amphigory (2009) may be as good an exemplar as any. Given its UK première on 13 August by the talented British violist Lawrence Power, with the Philharmonia Orchestra under Susanna Mälkki, the concerto's Proms appearance marks the first time the festival has put on any of her pieces.