fact: Definition cEx := \sum_(r <- fin_img X) r * Pr P (finset (X @^-1 r) :&: F) / Pr P F.
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