fact: Definition lin1_mx (f : 'rV[R]_m -> 'rV[R]_n) := \matrix[lin1_mx_key]_(i, j) f (delta_mx 0 i) 0 j.
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)