proposition: Lemma pr_eqE (X : {RV P -> A}) (a : A) : `Pr[ X = a ] = Pr P (finset (X @^-1 a)).
proof: Proof. by rewrite /pr_eq; unlock. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum matrix) mathcomp(Rstruct reals) Reals Lra ssrR Reals_ext realType_ext logb ssr_ext ssralg_ext bigop_ext fdist