theorem
  for M being Matrix of 0,m,D holds len M = 0 & width M = 0 & Indices M = {}
proof
  let M be Matrix of 0,m,D;
  len M = 0 by Def2;
  then width M = 0 by Def3;
  then Seg width M = 0;
  hence thesis by Def2,ZFMISC_1:90;
end;
