fact: Definition f (a : A) := [ffun b => if b is Some a' then if a == a' then p.~ else 0 else p].
imports: mathcomp(all_ssreflect all_algebra matrix) Reals mathcomp(mathcomp_extra Rstruct) ssrR Reals_ext realType_ext ssr_ext ssralg_ext logb fdist entropy binary_entropy_function channel hamming channel_code