reserve a,b,c for set;

theorem
  for X,x0,x being set st x in X holds {x} is closed Subset of
  DiscrWithInfin(X,x0)
proof
  let X,x0,x be set;
  set T = DiscrWithInfin(X,x0);
  the carrier of T = X by Def5;
  hence thesis by Th20,ZFMISC_1:31;
end;
