Experimental ensemble directed by Petr Kotík, started upon his return to Prague from his studies in Vienna in 1966. Other members included Josef Vejvoda, Jan Hynčica, Pavel Kondelík, and Václav Zahradník. It was the first live electronics group in Prague, and lasted until 1969.
"Kotik met Cornelius Cardew in Warsaw in 1962, and they began exchanging scores by mail, including Treatise, which was a work in progress. Upon meeting again in London (1966), Cardew provided Kotik with additional portions of the score and insights. Fresh from this encounter, Kotik started the QUaX Ensemble. The first thing QUaX did was to rehearse Treatise, working through the pages Kotik had: 'The piece was very important for getting all of us together, musically speaking, besides having a lot of fun working out individual pages by having all the musicians contribute ideas and suggestions. We worked regularly over a long period of time, ending up with a 2-hour version of the piece ... only performed once, at the concert on October 15, 1967 in Prague,'" with four other members of the ensemble (source). The recording was released in 2009 by Mode Records.