fact: Definition rcutmx (A : 'M_(m, n1 + n2)) := \matrix_(i < m, j < n2) (A i (rshift n1 j) : R).
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms