fact: Definition idealr_closed (R : ringType) (S : {pred R}) := [/\ 0 \in S, 1 \notin S & forall a, {in S &, forall u v, a * u + v \in S}].
imports: HB(structures) mathcomp(ssreflect eqtype choice ssreflect ssrbool ssrnat) mathcomp(ssrfun seq ssralg generic_quotient)