fact: Definition mxcol n (B_ : forall i, 'M[T]_(p_ i, n)) := \matrix_(j, k) B_ (sig1 j) (sig2 j) k.
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)