@Unpublished{DJDHughes:units,
  author    =  {Hughes, Dominic J.D.},
  title     =  {Simple multiplicative proof nets with units},
  year      =  {2005},
  month     =  {March},
  note      =  {Archived as math.LO/0507003 at arXiv.org.  Submitted.}
}