fact: Example Kostka_expl3 : Kostka_rec [:: 4; 4; 3; 1] [:: 3; 3; 2; 2; 1; 1] == 25.
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