fact: Variable char_poly_mxC : forall n, mxC n n -> mxpolyC n n.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path ssralg) mathcomp(fintype perm choice matrix bigop zmodp poly polydiv mxpoly) CoqEAL(minor hrel param refinements seqmx)