@unpublished{perszyk-smith01,
   author =  {Ken Perszyk and Nicholas J.J. Smith},
   title =   {The Paradoxes of Time Travel},
   note =    {Text of a lecture presented at Te Papa (National Museum of New Zealand),
             \url{http://www-personal.usyd.edu.au/~njjsmith/papers/te_papa.pdf}},
   year =    2001,
}