fact: Definition submxblock (A : 'M[T]_(sp, sq)) i j := mxsub (Rank i) (Rank j) A.
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)