anchor.diff:  	false ->
   	    case check_liveness_at(R, Fail, St0) of
   		{killed,St1} ->
  +		    check_liveness(R, Is, St1);
  +		{exit_not_used,St1} ->
   		    check_liveness(R, Is, St1);
   		{not_used,St1} ->
   		    not_used(check_liveness(R, Is, St1));
  
positive.code: 	    {killed,St0};
  	true ->
  	    case check_liveness_block_1(R, Ss, Ds, Op, Is, St0) of
  		{killed,St} -> {not_used,St};
                  {transparent,St} -> {alloc_used,St};
  		{_,_}=Res -> Res
  	    end
      end;
  check_liveness_block({y,_}=R, [{set,Ds,Ss,{alloc,_Live,Op}}|Is], St) ->
      check_liveness_block_1(R, Ss, Ds, Op, Is, St);
  check_liveness_block(R, [{set,Ds,Ss,Op}|Is], St) ->
      check_liveness_block_1(R, Ss, Ds, Op, Is, St);
  check_liveness_block(_, [], St) -> {transparent,St}.
  
negative.code:     St = #live{lbl=D,res=gb_trees:empty()},
      case check_liveness(R, Is, St) of
  	{used,_} -> false;
  	{exit_not_used,_} -> false;
  	{_,_} -> true
      end.
  
  