@InProceedings{HG03,
  author    =  {Hughes, D. J. D., and R. J.~van Glabbeek},
  title     =  {Proof Nets for unit-free Multiplicative-Additive Linear Logic
               ({E}xtended abstract)},
  booktitle =  {Proc.\ IEEE Logic in Computer Science},  
  year      =  {2003},
  note      =  {With proofs appended, available on Hughes' web site}
}