anchor.diff:  %% @doc
   %% @end
   %% -----------------------------------------------------------------------------
  +-spec add(node_spec(), Actor :: actor(), t()) -> t().
  +
   add(#{name := _} = NodeSpec, Actor, T0) ->
       {ok, T} = state_orset:mutate({add, NodeSpec}, Actor, T0),
       T.
  
positive.code: %% @doc
  %% @end
  %% -----------------------------------------------------------------------------
  equal(T1, T2) ->
      state_orset:equal(T1, T2).
  
  
negative.code: %% @doc
  %% @end
  %% -----------------------------------------------------------------------------
  -spec new() -> t().
  
  new() ->
      state_orset:new().
  
  