fact: Definition prev_root (p : {poly R}) a x := if p == 0 then x else last (minr a x) (roots p a x).
imports: mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq choice fintype) mathcomp(bigop order ssralg poly polydiv ssrnum zmodp) mathcomp(polyorder path interval ssrint)