@Manual{tikzpgf2.10,
  title = 	 {TikZ \& PGF, Manual for Version 2.10},
  author = 	 {Till Tantau},
  year = 	 2007,
  url = {http://sourceforge.net/projects/pgf}
}

@book{texbook,
  author =  "Donald E. Knuth",
  title =   "The {TeX}book",
  publisher =   "Addison-Wesley",
  year =  1996,
}

@Manual{tikzpgf3.0.0,
  title = 	 {TikZ \& PGF, Manual for Version 3.0.0},
  author = 	 {Till Tantau},
  year = 	 2013,
  url = {http://sourceforge.net/projects/pgf}
}