 reserve n,i,k,m for Nat;
 reserve p for Prime;

theorem
  for Z being Subset of REAL st 0 in Z holds
    (id Z)"{0} = {0}
  proof
    let Z be Subset of REAL;
    assume 0 in Z; then
    {0} c= Z by ZFMISC_1:31;
    hence thesis by FUNCT_2:94;
  end;
