reserve D for non empty set,
  i,j,k for Nat,
  n,m for Nat,
  r for Real,
  e for real-valued FinSequence;

theorem Th23:
  for M be Matrix of REAL st len M = 0 holds SumAll M = 0
proof
  let M be Matrix of REAL;
  assume len M = 0;
  then len Sum M = 0 by Def1;
  then Sum M = <*>REAL;
  hence thesis by RVSUM_1:72;
end;
