fact: Definition mxvec_index (i : 'I_m) (j : 'I_n) := cast_ord mxvec_cast (enum_rank (i, 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)