anchor.diff:  
           %% Determine depth.
           Depth = depth(Dag, Dst, 0),
  -        lager:info("Depth of ~p is ~p", [V, Depth]),
   
           %% Re-create destination vertex with new depth.
           case digraph:vertex(Dag, Dst) of
  
positive.code: add_vertices(Vs) ->
      gen_server:call(?MODULE, {add_vertices, Vs}, infinity).
  
  %% @doc Check if linking the given vertices will form a loop.
  %%
  %%      The user may accidentally form a loop while writing a dataflow
  
negative.code: %% API
  -export([start_link/0,
           will_form_cycle/2,
           vertices/0,
           add_edges/6,
           add_vertex/1,
           add_vertices/1]).
  