@book{LNCS2283,author={Tobias Nipkow and Lawrence Paulson and Markus Wenzel},
title="Isabelle/HOL --- A Proof Assistant for Higher-Order Logic",
publisher=Springer,series=LNCS,volume=2283,year=2002,
note={\url{http://www.in.tum.de/~nipkow/LNCS2283/}}}


@article{website:isabelle_archive_shortest_path,
  author =   {Benedikt Nordhoff and  Peter Lammich},
  title =    {Dijkstra's Shortest Path Algorithm},
  journal =  {Archive of Formal Proofs},
  month =    Jun,
  year =     2012,
  note =     {\url{http://isa-afp.org/entries/Dijkstra_Shortest_Path.shtml}, Formal proof development},
  ISSN =     {2150-914x}
}

@online{koni_proof_lecture_notes,
    author    = "Francisco Martin",
    title     = "The {S}even {B}ridges of {K}{\"o}nigsberg",
   	howpublished = "\url{http://www.ugr.es/~fmartin/gi/bridges.pdf}",
   	lastchecked = {14.01.2013}
}


@article{friend_combitorial,
title = "The friendship theorem ",
journal = "Indagationes Mathematicae (Proceedings) ",
volume = "75",
number = "3",
pages = "257 - 262",
year = "1972",
note = "",
issn = "1385-7258",
doi = "10.1016/1385-7258(72)90063-7",
url = "http://www.sciencedirect.com/science/article/pii/1385725872900637",
author = "Judith Q Longyear and T.D Parsons"
}

@article{mertzios2008friendship,
  title={The friendship problem on graphs.},
  author={Mertzios, George B and Unger, Walter},
  year={2008},
  publisher={DU}
}
