@Book{Anderberg:1973:CAA,
  author =       "Michael R. Anderberg",
  title =	"Cluster Analysis for Applications",
  year =	 "1973",
  publisher =    "Academic Press",
  address =      "New York",
}
@gr-article{Koko05,
   author="Κοκορέτσης Κοψιδάκιας και Ποτήρης Κρασοκανάτας",
   title="Εξόρυξη Κοψιδιών: μια συνολοθεωρητική προσέγγιση",
   year="2005",
   publisher="Burned Out Press",
   address="Athens",
}