fact: Definition num_occ_dist := seq_nat_fdist (sum_num_occ_size S) S_nonempty.
imports: mathcomp(all_ssreflect ssralg ssrnum) Reals mathcomp(Rstruct) ssrR realType_ext Reals_ext ssr_ext ssralg_ext logb fdist entropy convex ln_facts jensen num_occ