Comment on "Spin Dynamics of the 2D Spin 1/2 Quantum Antiferromagnet   Copper Deuteroformate Tetradeuterate (CFTD)"
  Comment on "Spin Dynamics of the 2D Spin 1/2 Quantum Antiferromagnet Copper Deuteroformate Tetradeuterate (CFTD)", H. M. Ronnow et al., Phys. Rev. Lett. 87, 037202 (2001) 
Peter Kopietz and Ivan Spremo