reserve W for Universe,
  H for ZF-formula,
  x,y,z,X for set,
  k for Variable,
  f for Function of VAR,W,
  u,v for Element of W;

theorem Th4:
  W |= the_axiom_of_power_sets
proof
   for u holds W /\ bool u in W by CLASSES1:def 1,XBOOLE_1:17;
  hence thesis by ZFMODEL1:8;
end;
