theorem
  H is conjunctive implies for f holds f in St(the_left_argument_of H,E)
  & f in St(the_right_argument_of H,E) iff f in St(H,E)
proof
  assume H is conjunctive;
  then H = (the_left_argument_of H) '&' the_right_argument_of H by ZF_LANG:40;
  hence thesis by Th5;
end;
