@article{  
   author = {P. Baldi, E.B. Baum},
   title = {Bounds on the Size of Ultrametric Structures.},
   journal = {Physical Review Letters},
   volume = {56},
   number = {15},
   pages = {1598-1600},
   note = {},
   abstract = {},
   keywords = {},
   year = {1986}
}