proposition: Lemma surjective_in_contravariant : forall D E f, included D E -> surjective_in E f -> surjective_in D f.
proof: Proof. intros D E f inc f_surj y y_in ; apply f_surj ; try apply inc ; assumption. Qed.
imports: Rbase Ranalysis Rinterval Rfunctions Rfunction_def Ranalysis_def Rfunction_facts MyRIneq MyR_dist Lra