Beethoven's 10th Symphony--or, at least, a movement of it--made its belated debut in London Tuesday night, and initial critical reaction was hardly an ode to joy. The piece--the result of five years' work by musicologist Barry Cooper--was generally agreed to be "Beethovenian," but the authenticity of the work was brought into question repeatedly. "(Cooper's) statement that 'about two-thirds of it is based directly on Beethoven's sketches' begs an awful lot of questions, especially when we are concerned with a composer of such notoriously untidy working habits," wrote Paul Griffiths in the Times of London. Countered the Guardian's Edward Greenfield: "Though even Dr. Cooper would never assert that it was what Beethoven would finally have delivered . . . I marvel that the long Andante sections which framed this unexpectedly structured movement are so genuinely Beethovenian." Walter Weller conducted the Royal Liverpool Philharmonic Orchestra in the 162-year-old work's premiere at Royal Festival Hall. Added violinist/conductor Sir Yehudi Menuhin, who conducted the second half of the concert: "I think it is a valuable work. It is certainly Beethoven. I have huge admiration and respect for Dr. Cooper, who has done an extremely good job."