fact: Definition is_scalar_mx (A : 'M[V]_n) := if insub 0 is Some i then A == (A i i)%:M else true.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)