anchor.diff:  assert_term(Src, Vst) ->
       get_term_type(Src, Vst),
       ok.
  +
  +assert_not_literal({x,_}) -> ok;
  +assert_not_literal({y,_}) -> ok;
  +assert_not_literal(Literal) -> error({literal_not_allowed,Literal}).
   
   %% The possible types.
   %%
  
positive.code: 	    error({bad_type,Type})
      end;
  valfun_1({get_list,Src,D1,D2}, Vst0) ->
      assert_type(cons, Src, Vst0),
      Vst = set_type_reg(term, Src, D1, Vst0),
      set_type_reg(term, Src, D2, Vst);
  valfun_1({get_hd,Src,Dst}, Vst) ->
      assert_type(cons, Src, Vst),
      set_type_reg(term, Src, Dst, Vst);
  valfun_1({get_tl,Src,Dst}, Vst) ->
      assert_type(cons, Src, Vst),
      set_type_reg(term, Src, Dst, Vst);
  valfun_1({get_tuple_element,Src,I,Dst}, Vst) ->
      assert_type({tuple_element,I+1}, Src, Vst),
      set_type_reg(term, Src, Dst, Vst);
  valfun_1({jump,{f,Lbl}}, Vst) ->
  
negative.code:     error(unknown_instruction).
  
  verify_get_map(Fail, Src, List, Vst0) ->
      assert_not_literal(Src),                    %OTP 22.
      assert_type(map, Src, Vst0),
      Vst1 = foldl(fun(D, Vsti) ->
                           case is_reg_defined(D,Vsti) of
  