fact: Variables (X : 'rV[A]_n.+2 -> R) (X1 : A -> R) (X2 : 'rV[A]_n.+1 -> R).
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