(** h is an analysis of g if h could be an analysis of g and 
   if for all other candidates h' which could be an analysis of g, 
   h is included in h' *)
Definition is_analysis (g h : hedge) :=
  analysis_cond g h /\
  (forall h' : hedge, analysis_cond g h' -> inclusion h h').

Lemma analysis_analysed : forall g h h' : hedge, is_analysis g h -> is_analysis h h' -> equal h h'.