proposition: Lemma map_mpoly_issym (f : {sympoly R[n]}) : map_mpoly mor f \is symmetric.
proof: Proof. apply/issymP => s. by rewrite msym_map_mpoly (issymP _ (sympolP f)). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(ssralg ssrint fingroup perm) mathcomp(ssrcomplements freeg mpoly) sorted tools ordtype permuted partition skewpart composition Yamanouchi std tableau stdtab skewtab permcent antisym Schur_mpoly therule Schur_altdef unitriginv