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

theorem Th29:
  for M be Matrix of REAL holds SumAll M = Sum ColSum M
proof
  let M be Matrix of REAL;
  thus Sum ColSum M = SumAll (M@) by Th22
    .= SumAll M by Th28;
end;
