Inductive Power_set (A:Ensemble U) : Ensemble (Ensemble U) :=
    Definition_of_Power_set :
      forall X:Ensemble U, Included U X A -> In (Ensemble U) (Power_set A) X.Inductive Power_set (A:Ensemble U) : Ensemble (Ensemble U) :=
    Definition_of_Power_set :
      forall X:Ensemble U, Included U X A -> In (Ensemble U) (Power_set A) X.

Theorem Inclusion_is_transitive : Transitive (Ensemble U) (Included U).