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

theorem Th70:
  for A being Matrix of n,REAL holds (1_Rmatrix n)*A=A
proof
  let A be Matrix of n,REAL;
  n=len A by MATRIX_0:def 2;
  hence thesis by Th68;
end;
