fact: Definition in_fsetE := (@in_fset_ imfset_key, val_in_fset, in_fset0, in_fset1, in_fsetU, in_fsetI, in_fsetD, in_fsetM, in_fset1U, in_fsetD1).
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)