reserve x for set,
  D for non empty set,
  k,n,m,i,j,l for Nat,
  K for Field;

theorem
  for A being Matrix of REAL holds (n=width A implies A*(1_Rmatrix n)=A)
  & (m=len A implies (1_Rmatrix m)*A=A) by Th67,Th68;
