The QED structure of the photon                                                
  
 The structure of both quasi-real and highly virtual photons                   
 is investigated using the reaction e+e- --> e+e- mu+mu-,                      
 proceeding via the exchange of two photons. The results are based             
 on the complete OPAL dataset taken at e+e- centre-of-mass energies            
 close to the mass of the Z boson. The QED structure function                  
 and the differential cross-section for quasi-real photons are obtained        
 as functions of the fractional momentum x from the muon momentum              
 which is carried by the struck muon in the quasi-real photon for              
 values of Q^2 ranging from 1.5 to 400 GeV^2.                                  
 The differential cross-section for highly virtual photons is                  
 measured for 1.5 < Q^2 < 30 GeV^2 and 1.5 < P^2 < 20 GeV^2, where             
 Q^2 and P^2 are the negative values of the four-momentum squared of           
 the two photons such that Q^2 > P^2. Based on azimuthal correlations          
 the QED structure functions for quasi-real photons are determined for         
 an average Q^2 of 5.4 GeV^2.                                                  
  
 Parallel session : 2                  
 Plenary  session :12