fact: Definition cancel_both (fg : (A -> B) * (B -> A)) := cancel fg.1 fg.2 /\ cancel fg.2 fg.1.
imports: mathcomp(all_ssreflect ssralg ssrnum matrix) mathcomp(Rstruct) Reals ssrR Reals_ext logb ssr_ext ssralg_ext bigop_ext fdist proba