fact: Definition diff t1 t2 : n.-tuple T := [tuple of [seq x.1 `\` x.2 | x <- zip t1 t2]].
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)