fact: Definition setdiff (la mu : seq nat) : {set 'I_n} := [set i : 'I_n | nth 0 la i < nth 0 mu i].
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(ssralg ssrint fingroup perm) mathcomp(mpoly) tools combclass ordtype sorted partition tableau skewpart skewtab antisym Schur_mpoly freeSchur therule std stdtab unitriginv presentSn