proposition: Lemma dH_sym u v : dH u v = dH v u.
proof: Proof. by rewrite {1}/dH -wH_opp opprB. Qed.
imports: Reals mathcomp(all_ssreflect fingroup zmodp ssralg finalg perm matrix) mathcomp(poly mxalgebra mxpoly) mathcomp(Rstruct) ssr_ext ssralg_ext f2 num_occ natbin ssrR Reals_ext bigop_ext