o added missing operations in Ptmap (with the help of Francois Berenger)
  o fixed bug in Ptset/Hset (reported by Jan Midtgaard)
  o fixed bug in Ptset.Big (reported by Hugo Ferreira)
  o improved Heap.Functional
  o improved Ptset.filter and Hset.filter (contributed by Alain Frisch)
  o added function compare, equal and is_empty to Trie and Ptmap (ocaml 3.08)
    (code for Trie contributed by Francisco Valverde)
  o added Ptset.split and Ptset.intersect (code from Markus Mottl)
  o added covariance annotation for Ptmap.t (as suggested by Markus Mottl)

version 0.2, 14/5/2001
======================
  o fixed bug in Ptset.merge

version 0.1, 1/6/2000
=====================
  o first release