@article(AmCo
	,author  = "Amoia, V. and Cottafava, G."
	,title   = "Invariance Properties of Central Trees"
	,pages   = "465--467"
	,journal = "IEEE Transactions on Circuit Theory"
	,year    = "1971"
	,volume  = "CT-18"
	,number  = "4")

@book{ApHa
       ,author    = "Appel, Kenneth and Haken, Wolfgang"
       ,title     = "Every Map is Four Colorable"
       ,edition   = "first"
       ,publisher = "American Mathematical Society"
       ,location  = "Providence, Rhode Island"
       ,year      = "1989"}

@inproceedings{Mu
       ,author     = "Murata, Tsuyoshi"
       ,title      = "Discovery of {W}eb Communities Based on the Co-occurrence of
References"
       ,publisher  = "Springer-Verlag"
       ,proceeding = "Third International Conference on Discovery Science"
       ,series     = "Lecture Notes in Computer Science"
       ,booktitle  = "Lecture Notes in Artificial Intelligence"
       ,editors    = "Arikawa, Setsuo and Morishita, Shinichi"
       ,pages      = "65-75"
       ,year       = "2000"}