fact: Definition companionmx {R : ringType} (p : seq R) (d := (size p).-1) := \matrix_(i < d, j < d) if (i == d.-1 :> nat) then - p`_j else (i.+1 == j :> nat)%:R.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(div fintype tuple finfun bigop fingroup perm) mathcomp(ssralg zmodp matrix mxalgebra poly polydiv)