fact: Definition lin_mul_row u : 'M[R]_(m * n, n) := lin1_mx (mulmx u \o vec_mx).
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)