theorem Th19:
  len MX2FinS 1.(K,n) = n
proof
  MX2FinS 1.(K,n) is OrdBasis of n-VectSp_over K by MATRLIN2:45;
  hence len MX2FinS 1.(K,n)=dim(n-VectSp_over K) by MATRLIN2:21
   .=n by MATRIX13:112;
end;
