Nine movements, nearly an hour in length, Pierre Boulez’s Livre pour Quatuor, a work in progress for decades, is now fully performable thanks to the composer collaborating with the Diotima members in his final years, with the whole edited by Philippe Manoury who has also completed the fourth section. This is incredibly intensive music, in which every rigorous note, whether by bow or pizzicato, or other expressive means, such as trilling – none lost to Pentatone’s microphones – is significant, enhanced by these players’ palpable ‘insider’ dedication, technical assurance and meaningful, appositely precise interaction. Whether the musing/animated post-Webern Livre adds up (or is meant to) is another matter; trying to determine that imponderable must in itself be a work in progress, and I (we) have the best possible chance through this superb recording. Pentatone PTC 5187 360 is also the perfect Boulezian complement to Stefanovich’s stunning Second Sonata.