theorem Th11:
  for r being Real holds N is Reflexive & 0<r implies w in Ball(w,r)
proof
  let r be Real;
  assume N is Reflexive;
  then
A1: dist(w,w) = 0 by METRIC_1:1;
  assume 0<r;
  hence thesis by A1,METRIC_1:11;
end;
