fact: Definition is_algid e U := [/\ e \in U, e != 0 & {in U, forall u, e * u = u /\ u * e = u}].
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype div tuple finfun bigop ssralg) mathcomp(finalg zmodp matrix vector poly)