fact: Definition prod_rV n (x : 'rV[A]_n * 'rV[B]_n) : 'rV[A * B]_n := \row_(k < n) (x.1 ``_ k, x.2 ``_ k).
imports: mathcomp(all_ssreflect ssralg fingroup finalg perm zmodp) mathcomp(matrix mxalgebra vector) ssr_ext f2