theorem
  for M being Matrix of REAL st M = {} holds SumAll M = 0
proof
  let M be Matrix of REAL;
  assume M = {};
  then reconsider M1=M as Matrix of 0,width M,REAL by MATRIX_0:13;
  len M1 = 0 by MATRIX_0:22;
  hence thesis by MATRPROB:23;
end;
