reserve F,H,H9 for ZF-formula,
  x,y,z,t for Variable,
  a,b,c,d,A,X for set;

theorem
  for H holds (H is being_equality implies Free H = { Var1 H,Var2 H }) &
  (H is being_membership implies Free H = { Var1 H,Var2 H }) & (H is negative
  implies Free H = Free the_argument_of H) & (H is conjunctive implies Free H =
Free the_left_argument_of H \/ Free the_right_argument_of H) & (H is universal
  implies Free H = (Free the_scope_of H) \ { bound_in H })
proof
  let H;
  thus (H is being_equality implies Free H = { Var1 H,Var2 H } ) & (H is
being_membership implies Free H = { Var1 H,Var2 H } ) & (H is negative implies
  Free H = Free the_argument_of H ) by Lm2;
  thus H is conjunctive implies Free H = Free the_left_argument_of H \/ Free
  the_right_argument_of H
  proof
    assume H is conjunctive;
    hence Free H = union { Free the_left_argument_of H,Free
    the_right_argument_of H } by Lm2
      .= Free the_left_argument_of H \/ Free the_right_argument_of H by
ZFMISC_1:75;
  end;
  assume H is universal;
  hence thesis by Lm2;
end;
