proposition: Lemma fdistI_tperm (n : nat) (a b : 'I_n) : @fdistI_perm R n (fdist1 a) (tperm a b) = fdist1 b.
proof: Proof. apply/fdist_ext => /= x; rewrite fdistI_permE !fdist1E permE /=. case: ifPn => [/eqP ->|xa]; first by rewrite eq_sym. case: ifPn; by [rewrite eqxx | move=> _; rewrite (negbTE xa)]. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup perm matrix) mathcomp(all_algebra vector reals normedtype) mathcomp(mathcomp_extra boolp) mathcomp(Rstruct) ssrR logb realType_ext ssr_ext ssralg_ext bigop_ext