@book{book:4004309,
   title =     {Introduction to Algebraic and Constructive Quantum Field Theory},
   author =    {John C. Baez and Irving Ezra Segal and Zhengfang Zhou},
   publisher = {Princeton University Press},
   isbn =      {9781400862504},
   year =      {1992},
   series =    {Princeton Series in Physics},
   volume =    {},
}
@article{Wick1950,
 title     = {The Evaluation of the Collision Matrix},
 author    = {G. C. Wick},
 publisher = {American Physical Society},
 journal   = {Physical Review},
 issn      = {0031-899X,1536-6065},
 year      = {1950},
 volume    = {80},
 number     = {2},
 pages     = {268--272},
}
@article{Fewster1998,
 title     = {Bounds on negative energy densities in flat spacetime},
 author    = {C. J .Fewster and S. P. Eveson},
 publisher = {American Physical Society},
 journal   = {Physical Review D},
  ISSN = {1089-4918},
 year      = {1998},
 volume    = {58},
  number = {8},
  month = sep,
 pages     = {084010},
}