reserve a,x,y for object, A,B for set,
  l,m,n for Nat;

theorem Th6:
  for f being Function, a being set st a in dom f holds f|{a} = a
  .--> f.a
proof
  let f be Function, a be set;
  assume a in dom f;
  hence f|{a} = {[a,f.a]} by GRFUNC_1:28
    .= a .--> f.a by ZFMISC_1:29;
end;
